[PATCH 1/9] mm: workingset: don't drop refault information prematurely

[PATCH 1/9] mm: workingset: don't drop refault information prematurely

[Johannes Weiner]

From: Johannes Weiner <jweiner@fb.com>

If we keep just enough refault information to match the CURRENT page
cache during reclaim time, we could lose a lot of events when there is
only a temporary spike in non-cache memory consumption that pushes out
all the cache. Once cache comes back, we won't see those refaults.
They might not be actionable for LRU aging, but we want to know about
them for measuring memory pressure.

Signed-off-by: Johannes Weiner <jweiner@fb.com>
---
 mm/workingset.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/mm/workingset.c b/mm/workingset.c
index 40ee02c83978..53759a3cf99a 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -364,7 +364,7 @@ static unsigned long count_shadow_nodes(struct shrinker *shrinker,
 {
 	unsigned long max_nodes;
 	unsigned long nodes;
-	unsigned long cache;
+	unsigned long pages;
 
 	/* list_lru lock nests inside the IRQ-safe i_pages lock */
 	local_irq_disable();
@@ -393,14 +393,14 @@ static unsigned long count_shadow_nodes(struct shrinker *shrinker,
 	 *
 	 * PAGE_SIZE / radix_tree_nodes / node_entries * 8 / PAGE_SIZE
 	 */
-	if (sc->memcg) {
-		cache = mem_cgroup_node_nr_lru_pages(sc->memcg, sc->nid,
-						     LRU_ALL_FILE);
-	} else {
-		cache = node_page_state(NODE_DATA(sc->nid), NR_ACTIVE_FILE) +
-			node_page_state(NODE_DATA(sc->nid), NR_INACTIVE_FILE);
-	}
-	max_nodes = cache >> (RADIX_TREE_MAP_SHIFT - 3);
+#ifdef CONFIG_MEMCG
+	if (sc->memcg)
+		pages = page_counter_read(&sc->memcg->memory);
+	else
+#endif
+		pages = node_present_pages(sc->nid);
+
+	max_nodes = pages >> (RADIX_TREE_MAP_SHIFT - 3);
 
 	if (nodes <= max_nodes)
 		return 0;
-- 
2.18.0

[PATCH 2/9] mm: workingset: tell cache transitions from workingset thrashing

[Johannes Weiner]

Refaults happen during transitions between workingsets as well as
in-place thrashing. Knowing the difference between the two has a range
of applications, including measuring the impact of memory shortage on
the system performance, as well as the ability to smarter balance
pressure between the filesystem cache and the swap-backed workingset.

During workingset transitions, inactive cache refaults and pushes out
established active cache. When that active cache isn't stale, however,
and also ends up refaulting, that's bonafide thrashing.

Introduce a new page flag that tells on eviction whether the page has
been active or not in its lifetime. This bit is then stored in the
shadow entry, to classify refaults as transitioning or thrashing.

How many page->flags does this leave us with on 32-bit?

	20 bits are always page flags

	21 if you have an MMU

	23 with the zone bits for DMA, Normal, HighMem, Movable

	29 with the sparsemem section bits

	30 if PAE is enabled

	31 with this patch.

So on 32-bit PAE, that leaves 1 bit for distinguishing two NUMA
nodes. If that's not enough, the system can switch to discontigmem and
re-gain the 6 or 7 sparsemem section bits.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/mmzone.h         |  1 +
 include/linux/page-flags.h     |  5 +-
 include/linux/swap.h           |  2 +-
 include/trace/events/mmflags.h |  1 +
 mm/filemap.c                   |  9 ++--
 mm/huge_memory.c               |  1 +
 mm/memcontrol.c                |  2 +
 mm/migrate.c                   |  2 +
 mm/swap_state.c                |  1 +
 mm/vmscan.c                    |  1 +
 mm/vmstat.c                    |  1 +
 mm/workingset.c                | 95 ++++++++++++++++++++++------------
 12 files changed, 79 insertions(+), 42 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 32699b2dc52a..6af87946d241 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -163,6 +163,7 @@ enum node_stat_item {
 	NR_ISOLATED_FILE,	/* Temporary isolated pages from file lru */
 	WORKINGSET_REFAULT,
 	WORKINGSET_ACTIVATE,
+	WORKINGSET_RESTORE,
 	WORKINGSET_NODERECLAIM,
 	NR_ANON_MAPPED,	/* Mapped anonymous pages */
 	NR_FILE_MAPPED,	/* pagecache pages mapped into pagetables.
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index e34a27727b9a..7af1c3c15d8e 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -69,13 +69,14 @@
  */
 enum pageflags {
 	PG_locked,		/* Page is locked. Don't touch. */
-	PG_error,
 	PG_referenced,
 	PG_uptodate,
 	PG_dirty,
 	PG_lru,
 	PG_active,
+	PG_workingset,
 	PG_waiters,		/* Page has waiters, check its waitqueue. Must be bit #7 and in the same byte as "PG_locked" */
+	PG_error,
 	PG_slab,
 	PG_owner_priv_1,	/* Owner use. If pagecache, fs may use*/
 	PG_arch_1,
@@ -280,6 +281,8 @@ PAGEFLAG(Dirty, dirty, PF_HEAD) TESTSCFLAG(Dirty, dirty, PF_HEAD)
 PAGEFLAG(LRU, lru, PF_HEAD) __CLEARPAGEFLAG(LRU, lru, PF_HEAD)
 PAGEFLAG(Active, active, PF_HEAD) __CLEARPAGEFLAG(Active, active, PF_HEAD)
 	TESTCLEARFLAG(Active, active, PF_HEAD)
+PAGEFLAG(Workingset, workingset, PF_HEAD)
+	TESTCLEARFLAG(Workingset, workingset, PF_HEAD)
 __PAGEFLAG(Slab, slab, PF_NO_TAIL)
 __PAGEFLAG(SlobFree, slob_free, PF_NO_TAIL)
 PAGEFLAG(Checked, checked, PF_NO_COMPOUND)	   /* Used by some filesystems */
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 2417d288e016..d8c47dcdec6f 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -296,7 +296,7 @@ struct vma_swap_readahead {
 
 /* linux/mm/workingset.c */
 void *workingset_eviction(struct address_space *mapping, struct page *page);
-bool workingset_refault(void *shadow);
+void workingset_refault(struct page *page, void *shadow);
 void workingset_activation(struct page *page);
 
 /* Do not use directly, use workingset_lookup_update */
diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index a81cffb76d89..a1675d43777e 100644
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -88,6 +88,7 @@
 	{1UL << PG_dirty,		"dirty"		},		\
 	{1UL << PG_lru,			"lru"		},		\
 	{1UL << PG_active,		"active"	},		\
+	{1UL << PG_workingset,		"workingset"	},		\
 	{1UL << PG_slab,		"slab"		},		\
 	{1UL << PG_owner_priv_1,	"owner_priv_1"	},		\
 	{1UL << PG_arch_1,		"arch_1"	},		\
diff --git a/mm/filemap.c b/mm/filemap.c
index 0604cb02e6f3..bd36b7226cf4 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -915,12 +915,9 @@ int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
 		 * data from the working set, only to cache data that will
 		 * get overwritten with something else, is a waste of memory.
 		 */
-		if (!(gfp_mask & __GFP_WRITE) &&
-		    shadow && workingset_refault(shadow)) {
-			SetPageActive(page);
-			workingset_activation(page);
-		} else
-			ClearPageActive(page);
+		WARN_ON_ONCE(PageActive(page));
+		if (!(gfp_mask & __GFP_WRITE) && shadow)
+			workingset_refault(page, shadow);
 		lru_cache_add(page);
 	}
 	return ret;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index b9f3dbd885bd..c67ecf77ea8b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2370,6 +2370,7 @@ static void __split_huge_page_tail(struct page *head, int tail,
 			 (1L << PG_mlocked) |
 			 (1L << PG_uptodate) |
 			 (1L << PG_active) |
+			 (1L << PG_workingset) |
 			 (1L << PG_locked) |
 			 (1L << PG_unevictable) |
 			 (1L << PG_dirty)));
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2bd3df3d101a..c59519d600ea 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5283,6 +5283,8 @@ static int memory_stat_show(struct seq_file *m, void *v)
 		   stat[WORKINGSET_REFAULT]);
 	seq_printf(m, "workingset_activate %lu\n",
 		   stat[WORKINGSET_ACTIVATE]);
+	seq_printf(m, "workingset_restore %lu\n",
+		   stat[WORKINGSET_RESTORE]);
 	seq_printf(m, "workingset_nodereclaim %lu\n",
 		   stat[WORKINGSET_NODERECLAIM]);
 
diff --git a/mm/migrate.c b/mm/migrate.c
index 8c0af0f7cab1..a6a9114e62dc 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -682,6 +682,8 @@ void migrate_page_states(struct page *newpage, struct page *page)
 		SetPageActive(newpage);
 	} else if (TestClearPageUnevictable(page))
 		SetPageUnevictable(newpage);
+	if (PageWorkingset(page))
+		SetPageWorkingset(newpage);
 	if (PageChecked(page))
 		SetPageChecked(newpage);
 	if (PageMappedToDisk(page))
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 07f9aa2340c3..2721ef8862d1 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -451,6 +451,7 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 			/*
 			 * Initiate read into locked page and return.
 			 */
+			SetPageWorkingset(new_page);
 			lru_cache_add_anon(new_page);
 			*new_page_allocated = true;
 			return new_page;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9270a4370d54..8d1ad48ffbcd 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1976,6 +1976,7 @@ static void shrink_active_list(unsigned long nr_to_scan,
 		}
 
 		ClearPageActive(page);	/* we are de-activating */
+		SetPageWorkingset(page);
 		list_add(&page->lru, &l_inactive);
 	}
 
diff --git a/mm/vmstat.c b/mm/vmstat.c
index a2b9518980ce..507dc9c01b88 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1145,6 +1145,7 @@ const char * const vmstat_text[] = {
 	"nr_isolated_file",
 	"workingset_refault",
 	"workingset_activate",
+	"workingset_restore",
 	"workingset_nodereclaim",
 	"nr_anon_pages",
 	"nr_mapped",
diff --git a/mm/workingset.c b/mm/workingset.c
index 53759a3cf99a..ef6be3d92116 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -121,7 +121,7 @@
  * the only thing eating into inactive list space is active pages.
  *
  *
- *		Activating refaulting pages
+ *		Refaulting inactive pages
  *
  * All that is known about the active list is that the pages have been
  * accessed more than once in the past.  This means that at any given
@@ -134,6 +134,10 @@
  * used less frequently than the refaulting page - or even not used at
  * all anymore.
  *
+ * That means if inactive cache is refaulting with a suitable refault
+ * distance, we assume the cache workingset is transitioning and put
+ * pressure on the current active list.
+ *
  * If this is wrong and demotion kicks in, the pages which are truly
  * used more frequently will be reactivated while the less frequently
  * used once will be evicted from memory.
@@ -141,6 +145,14 @@
  * But if this is right, the stale pages will be pushed out of memory
  * and the used pages get to stay in cache.
  *
+ *		Refaulting active pages
+ *
+ * If on the other hand the refaulting pages have recently been
+ * deactivated, it means that the active list is no longer protecting
+ * actively used cache from reclaim. The cache is NOT transitioning to
+ * a different workingset; the existing workingset is thrashing in the
+ * space allocated to the page cache.
+ *
  *
  *		Implementation
  *
@@ -156,8 +168,7 @@
  */
 
 #define EVICTION_SHIFT	(RADIX_TREE_EXCEPTIONAL_ENTRY + \
-			 NODES_SHIFT +	\
-			 MEM_CGROUP_ID_SHIFT)
+			 1 + NODES_SHIFT + MEM_CGROUP_ID_SHIFT)
 #define EVICTION_MASK	(~0UL >> EVICTION_SHIFT)
 
 /*
@@ -170,23 +181,28 @@
  */
 static unsigned int bucket_order __read_mostly;
 
-static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction)
+static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
+			 bool workingset)
 {
 	eviction >>= bucket_order;
 	eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
 	eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
+	eviction = (eviction << 1) | workingset;
 	eviction = (eviction << RADIX_TREE_EXCEPTIONAL_SHIFT);
 
 	return (void *)(eviction | RADIX_TREE_EXCEPTIONAL_ENTRY);
 }
 
 static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
-			  unsigned long *evictionp)
+			  unsigned long *evictionp, bool *workingsetp)
 {
 	unsigned long entry = (unsigned long)shadow;
 	int memcgid, nid;
+	bool workingset;
 
 	entry >>= RADIX_TREE_EXCEPTIONAL_SHIFT;
+	workingset = entry & 1;
+	entry >>= 1;
 	nid = entry & ((1UL << NODES_SHIFT) - 1);
 	entry >>= NODES_SHIFT;
 	memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
@@ -195,6 +211,7 @@ static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
 	*memcgidp = memcgid;
 	*pgdat = NODE_DATA(nid);
 	*evictionp = entry << bucket_order;
+	*workingsetp = workingset;
 }
 
 /**
@@ -207,8 +224,8 @@ static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
  */
 void *workingset_eviction(struct address_space *mapping, struct page *page)
 {
-	struct mem_cgroup *memcg = page_memcg(page);
 	struct pglist_data *pgdat = page_pgdat(page);
+	struct mem_cgroup *memcg = page_memcg(page);
 	int memcgid = mem_cgroup_id(memcg);
 	unsigned long eviction;
 	struct lruvec *lruvec;
@@ -220,30 +237,30 @@ void *workingset_eviction(struct address_space *mapping, struct page *page)
 
 	lruvec = mem_cgroup_lruvec(pgdat, memcg);
 	eviction = atomic_long_inc_return(&lruvec->inactive_age);
-	return pack_shadow(memcgid, pgdat, eviction);
+	return pack_shadow(memcgid, pgdat, eviction, PageWorkingset(page));
 }
 
 /**
  * workingset_refault - evaluate the refault of a previously evicted page
+ * @page: the freshly allocated replacement page
  * @shadow: shadow entry of the evicted page
  *
  * Calculates and evaluates the refault distance of the previously
  * evicted page in the context of the node it was allocated in.
- *
- * Returns %true if the page should be activated, %false otherwise.
  */
-bool workingset_refault(void *shadow)
+void workingset_refault(struct page *page, void *shadow)
 {
 	unsigned long refault_distance;
+	struct pglist_data *pgdat;
 	unsigned long active_file;
 	struct mem_cgroup *memcg;
 	unsigned long eviction;
 	struct lruvec *lruvec;
 	unsigned long refault;
-	struct pglist_data *pgdat;
+	bool workingset;
 	int memcgid;
 
-	unpack_shadow(shadow, &memcgid, &pgdat, &eviction);
+	unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset);
 
 	rcu_read_lock();
 	/*
@@ -263,41 +280,51 @@ bool workingset_refault(void *shadow)
 	 * configurations instead.
 	 */
 	memcg = mem_cgroup_from_id(memcgid);
-	if (!mem_cgroup_disabled() && !memcg) {
-		rcu_read_unlock();
-		return false;
-	}
+	if (!mem_cgroup_disabled() && !memcg)
+		goto out;
 	lruvec = mem_cgroup_lruvec(pgdat, memcg);
 	refault = atomic_long_read(&lruvec->inactive_age);
 	active_file = lruvec_lru_size(lruvec, LRU_ACTIVE_FILE, MAX_NR_ZONES);
 
 	/*
-	 * The unsigned subtraction here gives an accurate distance
-	 * across inactive_age overflows in most cases.
+	 * Calculate the refault distance
 	 *
-	 * There is a special case: usually, shadow entries have a
-	 * short lifetime and are either refaulted or reclaimed along
-	 * with the inode before they get too old.  But it is not
-	 * impossible for the inactive_age to lap a shadow entry in
-	 * the field, which can then can result in a false small
-	 * refault distance, leading to a false activation should this
-	 * old entry actually refault again.  However, earlier kernels
-	 * used to deactivate unconditionally with *every* reclaim
-	 * invocation for the longest time, so the occasional
-	 * inappropriate activation leading to pressure on the active
-	 * list is not a problem.
+	 * The unsigned subtraction here gives an accurate distance
+	 * across inactive_age overflows in most cases. There is a
+	 * special case: usually, shadow entries have a short lifetime
+	 * and are either refaulted or reclaimed along with the inode
+	 * before they get too old.  But it is not impossible for the
+	 * inactive_age to lap a shadow entry in the field, which can
+	 * then can result in a false small refault distance, leading
+	 * to a false activation should this old entry actually
+	 * refault again.  However, earlier kernels used to deactivate
+	 * unconditionally with *every* reclaim invocation for the
+	 * longest time, so the occasional inappropriate activation
+	 * leading to pressure on the active list is not a problem.
 	 */
 	refault_distance = (refault - eviction) & EVICTION_MASK;
 
 	inc_lruvec_state(lruvec, WORKINGSET_REFAULT);
 
-	if (refault_distance <= active_file) {
-		inc_lruvec_state(lruvec, WORKINGSET_ACTIVATE);
-		rcu_read_unlock();
-		return true;
+	/*
+	 * Compare the distance to the existing workingset size. We
+	 * don't act on pages that couldn't stay resident even if all
+	 * the memory was available to the page cache.
+	 */
+	if (refault_distance > active_file)
+		goto out;
+
+	SetPageActive(page);
+	atomic_long_inc(&lruvec->inactive_age);
+	inc_lruvec_state(lruvec, WORKINGSET_ACTIVATE);
+
+	/* Page was active prior to eviction */
+	if (workingset) {
+		SetPageWorkingset(page);
+		inc_lruvec_state(lruvec, WORKINGSET_RESTORE);
 	}
+out:
 	rcu_read_unlock();
-	return false;
 }
 
 /**
-- 
2.18.0

Re: [PATCH 2/9] mm: workingset: tell cache transitions from workingset thrashing

[Johannes Weiner]

Hi Suren,

On Wed, Aug 01, 2018 at 02:56:27PM -0700, Suren Baghdasaryan wrote:
> On Wed, Aug 1, 2018 at 8:19 AM, Johannes Weiner <hannes@cmpxchg.org> wrote:
> >         /*
> > -        * The unsigned subtraction here gives an accurate distance
> > -        * across inactive_age overflows in most cases.
> > +        * Calculate the refault distance
> >          *
> > -        * There is a special case: usually, shadow entries have a
> > -        * short lifetime and are either refaulted or reclaimed along
> > -        * with the inode before they get too old.  But it is not
> > -        * impossible for the inactive_age to lap a shadow entry in
> > -        * the field, which can then can result in a false small
> > -        * refault distance, leading to a false activation should this
> > -        * old entry actually refault again.  However, earlier kernels
> > -        * used to deactivate unconditionally with *every* reclaim
> > -        * invocation for the longest time, so the occasional
> > -        * inappropriate activation leading to pressure on the active
> > -        * list is not a problem.
> > +        * The unsigned subtraction here gives an accurate distance
> > +        * across inactive_age overflows in most cases. There is a
> > +        * special case: usually, shadow entries have a short lifetime
> > +        * and are either refaulted or reclaimed along with the inode
> > +        * before they get too old.  But it is not impossible for the
> > +        * inactive_age to lap a shadow entry in the field, which can
> > +        * then can result in a false small refault distance, leading
> 
> "which can then can" - please remove one of the "can".

Good catch, will fix.

[PATCH 3/9] delayacct: track delays from thrashing cache pages

[Johannes Weiner]

Delay accounting already measures the time a task spends in direct
reclaim and waiting for swapin, but in low memory situations tasks
spend can spend a significant amount of their time waiting on
thrashing page cache. This isn't tracked right now.

To know the full impact of memory contention on an individual task,
measure the delay when waiting for a recently evicted active cache
page to read back into memory.

Also update tools/accounting/getdelays.c:

     [hannes@computer accounting]$ sudo ./getdelays -d -p 1
     print delayacct stats ON
     PID     1

     CPU             count     real total  virtual total    delay total  delay average
                     50318      745000000      847346785      400533713          0.008ms
     IO              count    delay total  delay average
                       435      122601218              0ms
     SWAP            count    delay total  delay average
                         0              0              0ms
     RECLAIM         count    delay total  delay average
                         0              0              0ms
     THRASHING       count    delay total  delay average
                        19       12621439              0ms

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/delayacct.h      | 23 +++++++++++++++++++++++
 include/uapi/linux/taskstats.h |  6 +++++-
 kernel/delayacct.c             | 15 +++++++++++++++
 mm/filemap.c                   | 11 +++++++++++
 tools/accounting/getdelays.c   |  8 +++++++-
 5 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/include/linux/delayacct.h b/include/linux/delayacct.h
index 5e335b6203f4..d3e75b3ba487 100644
--- a/include/linux/delayacct.h
+++ b/include/linux/delayacct.h
@@ -57,7 +57,12 @@ struct task_delay_info {
 
 	u64 freepages_start;
 	u64 freepages_delay;	/* wait for memory reclaim */
+
+	u64 thrashing_start;
+	u64 thrashing_delay;	/* wait for thrashing page */
+
 	u32 freepages_count;	/* total count of memory reclaim */
+	u32 thrashing_count;	/* total count of thrash waits */
 };
 #endif
 
@@ -76,6 +81,8 @@ extern int __delayacct_add_tsk(struct taskstats *, struct task_struct *);
 extern __u64 __delayacct_blkio_ticks(struct task_struct *);
 extern void __delayacct_freepages_start(void);
 extern void __delayacct_freepages_end(void);
+extern void __delayacct_thrashing_start(void);
+extern void __delayacct_thrashing_end(void);
 
 static inline int delayacct_is_task_waiting_on_io(struct task_struct *p)
 {
@@ -156,6 +163,18 @@ static inline void delayacct_freepages_end(void)
 		__delayacct_freepages_end();
 }
 
+static inline void delayacct_thrashing_start(void)
+{
+	if (current->delays)
+		__delayacct_thrashing_start();
+}
+
+static inline void delayacct_thrashing_end(void)
+{
+	if (current->delays)
+		__delayacct_thrashing_end();
+}
+
 #else
 static inline void delayacct_set_flag(int flag)
 {}
@@ -182,6 +201,10 @@ static inline void delayacct_freepages_start(void)
 {}
 static inline void delayacct_freepages_end(void)
 {}
+static inline void delayacct_thrashing_start(void)
+{}
+static inline void delayacct_thrashing_end(void)
+{}
 
 #endif /* CONFIG_TASK_DELAY_ACCT */
 
diff --git a/include/uapi/linux/taskstats.h b/include/uapi/linux/taskstats.h
index b7aa7bb2349f..5e8ca16a9079 100644
--- a/include/uapi/linux/taskstats.h
+++ b/include/uapi/linux/taskstats.h
@@ -34,7 +34,7 @@
  */
 
 
-#define TASKSTATS_VERSION	8
+#define TASKSTATS_VERSION	9
 #define TS_COMM_LEN		32	/* should be >= TASK_COMM_LEN
 					 * in linux/sched.h */
 
@@ -164,6 +164,10 @@ struct taskstats {
 	/* Delay waiting for memory reclaim */
 	__u64	freepages_count;
 	__u64	freepages_delay_total;
+
+	/* Delay waiting for thrashing page */
+	__u64	thrashing_count;
+	__u64	thrashing_delay_total;
 };
 
 
diff --git a/kernel/delayacct.c b/kernel/delayacct.c
index e2764d767f18..02ba745c448d 100644
--- a/kernel/delayacct.c
+++ b/kernel/delayacct.c
@@ -134,9 +134,12 @@ int __delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk)
 	d->swapin_delay_total = (tmp < d->swapin_delay_total) ? 0 : tmp;
 	tmp = d->freepages_delay_total + tsk->delays->freepages_delay;
 	d->freepages_delay_total = (tmp < d->freepages_delay_total) ? 0 : tmp;
+	tmp = d->thrashing_delay_total + tsk->delays->thrashing_delay;
+	d->thrashing_delay_total = (tmp < d->thrashing_delay_total) ? 0 : tmp;
 	d->blkio_count += tsk->delays->blkio_count;
 	d->swapin_count += tsk->delays->swapin_count;
 	d->freepages_count += tsk->delays->freepages_count;
+	d->thrashing_count += tsk->delays->thrashing_count;
 	spin_unlock_irqrestore(&tsk->delays->lock, flags);
 
 	return 0;
@@ -168,3 +171,15 @@ void __delayacct_freepages_end(void)
 		&current->delays->freepages_count);
 }
 
+void __delayacct_thrashing_start(void)
+{
+	current->delays->thrashing_start = ktime_get_ns();
+}
+
+void __delayacct_thrashing_end(void)
+{
+	delayacct_end(&current->delays->lock,
+		      &current->delays->thrashing_start,
+		      &current->delays->thrashing_delay,
+		      &current->delays->thrashing_count);
+}
diff --git a/mm/filemap.c b/mm/filemap.c
index bd36b7226cf4..e49961e13dd9 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -36,6 +36,7 @@
 #include <linux/cleancache.h>
 #include <linux/shmem_fs.h>
 #include <linux/rmap.h>
+#include <linux/delayacct.h>
 #include "internal.h"
 
 #define CREATE_TRACE_POINTS
@@ -1073,8 +1074,15 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 {
 	struct wait_page_queue wait_page;
 	wait_queue_entry_t *wait = &wait_page.wait;
+	bool thrashing = false;
 	int ret = 0;
 
+	if (bit_nr == PG_locked && !PageSwapBacked(page) &&
+	    !PageUptodate(page) && PageWorkingset(page)) {
+		delayacct_thrashing_start();
+		thrashing = true;
+	}
+
 	init_wait(wait);
 	wait->flags = lock ? WQ_FLAG_EXCLUSIVE : 0;
 	wait->func = wake_page_function;
@@ -1113,6 +1121,9 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 
 	finish_wait(q, wait);
 
+	if (thrashing)
+		delayacct_thrashing_end();
+
 	/*
 	 * A signal could leave PageWaiters set. Clearing it here if
 	 * !waitqueue_active would be possible (by open-coding finish_wait),
diff --git a/tools/accounting/getdelays.c b/tools/accounting/getdelays.c
index 9f420d98b5fb..8cb504d30384 100644
--- a/tools/accounting/getdelays.c
+++ b/tools/accounting/getdelays.c
@@ -203,6 +203,8 @@ static void print_delayacct(struct taskstats *t)
 	       "SWAP  %15s%15s%15s\n"
 	       "      %15llu%15llu%15llums\n"
 	       "RECLAIM  %12s%15s%15s\n"
+	       "      %15llu%15llu%15llums\n"
+	       "THRASHING%12s%15s%15s\n"
 	       "      %15llu%15llu%15llums\n",
 	       "count", "real total", "virtual total",
 	       "delay total", "delay average",
@@ -222,7 +224,11 @@ static void print_delayacct(struct taskstats *t)
 	       "count", "delay total", "delay average",
 	       (unsigned long long)t->freepages_count,
 	       (unsigned long long)t->freepages_delay_total,
-	       average_ms(t->freepages_delay_total, t->freepages_count));
+	       average_ms(t->freepages_delay_total, t->freepages_count),
+	       "count", "delay total", "delay average",
+	       (unsigned long long)t->thrashing_count,
+	       (unsigned long long)t->thrashing_delay_total,
+	       average_ms(t->thrashing_delay_total, t->thrashing_count));
 }
 
 static void task_context_switch_counts(struct taskstats *t)
-- 
2.18.0

[PATCH 4/9] sched: loadavg: consolidate LOAD_INT, LOAD_FRAC, CALC_LOAD

[Johannes Weiner]

There are several definitions of those functions/macros in places that
mess with fixed-point load averages. Provide an official version.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 .../platforms/cell/cpufreq_spudemand.c        |  2 +-
 arch/powerpc/platforms/cell/spufs/sched.c     |  9 +++-----
 arch/s390/appldata/appldata_os.c              |  4 ----
 drivers/cpuidle/governors/menu.c              |  4 ----
 fs/proc/loadavg.c                             |  3 ---
 include/linux/sched/loadavg.h                 | 21 +++++++++++++++----
 kernel/debug/kdb/kdb_main.c                   |  7 +------
 kernel/sched/loadavg.c                        | 15 -------------
 8 files changed, 22 insertions(+), 43 deletions(-)

diff --git a/arch/powerpc/platforms/cell/cpufreq_spudemand.c b/arch/powerpc/platforms/cell/cpufreq_spudemand.c
index 882944c36ef5..5d8e8b6bb1cc 100644
--- a/arch/powerpc/platforms/cell/cpufreq_spudemand.c
+++ b/arch/powerpc/platforms/cell/cpufreq_spudemand.c
@@ -49,7 +49,7 @@ static int calc_freq(struct spu_gov_info_struct *info)
 	cpu = info->policy->cpu;
 	busy_spus = atomic_read(&cbe_spu_info[cpu_to_node(cpu)].busy_spus);
 
-	CALC_LOAD(info->busy_spus, EXP, busy_spus * FIXED_1);
+	info->busy_spus = calc_load(info->busy_spus, EXP, busy_spus * FIXED_1);
 	pr_debug("cpu %d: busy_spus=%d, info->busy_spus=%ld\n",
 			cpu, busy_spus, info->busy_spus);
 
diff --git a/arch/powerpc/platforms/cell/spufs/sched.c b/arch/powerpc/platforms/cell/spufs/sched.c
index ccc421503363..70101510b19d 100644
--- a/arch/powerpc/platforms/cell/spufs/sched.c
+++ b/arch/powerpc/platforms/cell/spufs/sched.c
@@ -987,9 +987,9 @@ static void spu_calc_load(void)
 	unsigned long active_tasks; /* fixed-point */
 
 	active_tasks = count_active_contexts() * FIXED_1;
-	CALC_LOAD(spu_avenrun[0], EXP_1, active_tasks);
-	CALC_LOAD(spu_avenrun[1], EXP_5, active_tasks);
-	CALC_LOAD(spu_avenrun[2], EXP_15, active_tasks);
+	spu_avenrun[0] = calc_load(spu_avenrun[0], EXP_1, active_tasks);
+	spu_avenrun[1] = calc_load(spu_avenrun[1], EXP_5, active_tasks);
+	spu_avenrun[2] = calc_load(spu_avenrun[2], EXP_15, active_tasks);
 }
 
 static void spusched_wake(struct timer_list *unused)
@@ -1071,9 +1071,6 @@ void spuctx_switch_state(struct spu_context *ctx,
 	}
 }
 
-#define LOAD_INT(x) ((x) >> FSHIFT)
-#define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100)
-
 static int show_spu_loadavg(struct seq_file *s, void *private)
 {
 	int a, b, c;
diff --git a/arch/s390/appldata/appldata_os.c b/arch/s390/appldata/appldata_os.c
index 433a994b1a89..54f375627532 100644
--- a/arch/s390/appldata/appldata_os.c
+++ b/arch/s390/appldata/appldata_os.c
@@ -25,10 +25,6 @@
 
 #include "appldata.h"
 
-
-#define LOAD_INT(x) ((x) >> FSHIFT)
-#define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100)
-
 /*
  * OS data
  *
diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 1bfe03ceb236..3738b670df7a 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -133,10 +133,6 @@ struct menu_device {
 	int		interval_ptr;
 };
 
-
-#define LOAD_INT(x) ((x) >> FSHIFT)
-#define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100)
-
 static inline int get_loadavg(unsigned long load)
 {
 	return LOAD_INT(load) * 10 + LOAD_FRAC(load) / 10;
diff --git a/fs/proc/loadavg.c b/fs/proc/loadavg.c
index b572cc865b92..8bee50a97c0f 100644
--- a/fs/proc/loadavg.c
+++ b/fs/proc/loadavg.c
@@ -10,9 +10,6 @@
 #include <linux/seqlock.h>
 #include <linux/time.h>
 
-#define LOAD_INT(x) ((x) >> FSHIFT)
-#define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100)
-
 static int loadavg_proc_show(struct seq_file *m, void *v)
 {
 	unsigned long avnrun[3];
diff --git a/include/linux/sched/loadavg.h b/include/linux/sched/loadavg.h
index 80bc84ba5d2a..cc9cc62bb1f8 100644
--- a/include/linux/sched/loadavg.h
+++ b/include/linux/sched/loadavg.h
@@ -22,10 +22,23 @@ extern void get_avenrun(unsigned long *loads, unsigned long offset, int shift);
 #define EXP_5		2014		/* 1/exp(5sec/5min) */
 #define EXP_15		2037		/* 1/exp(5sec/15min) */
 
-#define CALC_LOAD(load,exp,n) \
-	load *= exp; \
-	load += n*(FIXED_1-exp); \
-	load >>= FSHIFT;
+/*
+ * a1 = a0 * e + a * (1 - e)
+ */
+static inline unsigned long
+calc_load(unsigned long load, unsigned long exp, unsigned long active)
+{
+	unsigned long newload;
+
+	newload = load * exp + active * (FIXED_1 - exp);
+	if (active >= load)
+		newload += FIXED_1-1;
+
+	return newload / FIXED_1;
+}
+
+#define LOAD_INT(x) ((x) >> FSHIFT)
+#define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100)
 
 extern void calc_global_load(unsigned long ticks);
 
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index e405677ee08d..a8f5aca5eb5e 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2556,16 +2556,11 @@ static int kdb_summary(int argc, const char **argv)
 	}
 	kdb_printf("%02ld:%02ld\n", val.uptime/(60*60), (val.uptime/60)%60);
 
-	/* lifted from fs/proc/proc_misc.c::loadavg_read_proc() */
-
-#define LOAD_INT(x) ((x) >> FSHIFT)
-#define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100)
 	kdb_printf("load avg   %ld.%02ld %ld.%02ld %ld.%02ld\n",
 		LOAD_INT(val.loads[0]), LOAD_FRAC(val.loads[0]),
 		LOAD_INT(val.loads[1]), LOAD_FRAC(val.loads[1]),
 		LOAD_INT(val.loads[2]), LOAD_FRAC(val.loads[2]));
-#undef LOAD_INT
-#undef LOAD_FRAC
+
 	/* Display in kilobytes */
 #define K(x) ((x) << (PAGE_SHIFT - 10))
 	kdb_printf("\nMemTotal:       %8lu kB\nMemFree:        %8lu kB\n"
diff --git a/kernel/sched/loadavg.c b/kernel/sched/loadavg.c
index a171c1258109..54fbdfb2d86c 100644
--- a/kernel/sched/loadavg.c
+++ b/kernel/sched/loadavg.c
@@ -91,21 +91,6 @@ long calc_load_fold_active(struct rq *this_rq, long adjust)
 	return delta;
 }
 
-/*
- * a1 = a0 * e + a * (1 - e)
- */
-static unsigned long
-calc_load(unsigned long load, unsigned long exp, unsigned long active)
-{
-	unsigned long newload;
-
-	newload = load * exp + active * (FIXED_1 - exp);
-	if (active >= load)
-		newload += FIXED_1-1;
-
-	return newload / FIXED_1;
-}
-
 #ifdef CONFIG_NO_HZ_COMMON
 /*
  * Handle NO_HZ for the global load-average.
-- 
2.18.0

[PATCH 5/9] sched: loadavg: make calc_load_n() public

[Johannes Weiner]

It's going to be used in a later patch. Keep the churn separate.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/sched/loadavg.h |   3 +
 kernel/sched/loadavg.c        | 138 +++++++++++++++++-----------------
 2 files changed, 72 insertions(+), 69 deletions(-)

diff --git a/include/linux/sched/loadavg.h b/include/linux/sched/loadavg.h
index cc9cc62bb1f8..4859bea47a7b 100644
--- a/include/linux/sched/loadavg.h
+++ b/include/linux/sched/loadavg.h
@@ -37,6 +37,9 @@ calc_load(unsigned long load, unsigned long exp, unsigned long active)
 	return newload / FIXED_1;
 }
 
+extern unsigned long calc_load_n(unsigned long load, unsigned long exp,
+				 unsigned long active, unsigned int n);
+
 #define LOAD_INT(x) ((x) >> FSHIFT)
 #define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100)
 
diff --git a/kernel/sched/loadavg.c b/kernel/sched/loadavg.c
index 54fbdfb2d86c..28a516575c18 100644
--- a/kernel/sched/loadavg.c
+++ b/kernel/sched/loadavg.c
@@ -91,6 +91,75 @@ long calc_load_fold_active(struct rq *this_rq, long adjust)
 	return delta;
 }
 
+/**
+ * fixed_power_int - compute: x^n, in O(log n) time
+ *
+ * @x:         base of the power
+ * @frac_bits: fractional bits of @x
+ * @n:         power to raise @x to.
+ *
+ * By exploiting the relation between the definition of the natural power
+ * function: x^n := x*x*...*x (x multiplied by itself for n times), and
+ * the binary encoding of numbers used by computers: n := \Sum n_i * 2^i,
+ * (where: n_i \elem {0, 1}, the binary vector representing n),
+ * we find: x^n := x^(\Sum n_i * 2^i) := \Prod x^(n_i * 2^i), which is
+ * of course trivially computable in O(log_2 n), the length of our binary
+ * vector.
+ */
+static unsigned long
+fixed_power_int(unsigned long x, unsigned int frac_bits, unsigned int n)
+{
+	unsigned long result = 1UL << frac_bits;
+
+	if (n) {
+		for (;;) {
+			if (n & 1) {
+				result *= x;
+				result += 1UL << (frac_bits - 1);
+				result >>= frac_bits;
+			}
+			n >>= 1;
+			if (!n)
+				break;
+			x *= x;
+			x += 1UL << (frac_bits - 1);
+			x >>= frac_bits;
+		}
+	}
+
+	return result;
+}
+
+/*
+ * a1 = a0 * e + a * (1 - e)
+ *
+ * a2 = a1 * e + a * (1 - e)
+ *    = (a0 * e + a * (1 - e)) * e + a * (1 - e)
+ *    = a0 * e^2 + a * (1 - e) * (1 + e)
+ *
+ * a3 = a2 * e + a * (1 - e)
+ *    = (a0 * e^2 + a * (1 - e) * (1 + e)) * e + a * (1 - e)
+ *    = a0 * e^3 + a * (1 - e) * (1 + e + e^2)
+ *
+ *  ...
+ *
+ * an = a0 * e^n + a * (1 - e) * (1 + e + ... + e^n-1) [1]
+ *    = a0 * e^n + a * (1 - e) * (1 - e^n)/(1 - e)
+ *    = a0 * e^n + a * (1 - e^n)
+ *
+ * [1] application of the geometric series:
+ *
+ *              n         1 - x^(n+1)
+ *     S_n := \Sum x^i = -------------
+ *             i=0          1 - x
+ */
+unsigned long
+calc_load_n(unsigned long load, unsigned long exp,
+	    unsigned long active, unsigned int n)
+{
+	return calc_load(load, fixed_power_int(exp, FSHIFT, n), active);
+}
+
 #ifdef CONFIG_NO_HZ_COMMON
 /*
  * Handle NO_HZ for the global load-average.
@@ -210,75 +279,6 @@ static long calc_load_nohz_fold(void)
 	return delta;
 }
 
-/**
- * fixed_power_int - compute: x^n, in O(log n) time
- *
- * @x:         base of the power
- * @frac_bits: fractional bits of @x
- * @n:         power to raise @x to.
- *
- * By exploiting the relation between the definition of the natural power
- * function: x^n := x*x*...*x (x multiplied by itself for n times), and
- * the binary encoding of numbers used by computers: n := \Sum n_i * 2^i,
- * (where: n_i \elem {0, 1}, the binary vector representing n),
- * we find: x^n := x^(\Sum n_i * 2^i) := \Prod x^(n_i * 2^i), which is
- * of course trivially computable in O(log_2 n), the length of our binary
- * vector.
- */
-static unsigned long
-fixed_power_int(unsigned long x, unsigned int frac_bits, unsigned int n)
-{
-	unsigned long result = 1UL << frac_bits;
-
-	if (n) {
-		for (;;) {
-			if (n & 1) {
-				result *= x;
-				result += 1UL << (frac_bits - 1);
-				result >>= frac_bits;
-			}
-			n >>= 1;
-			if (!n)
-				break;
-			x *= x;
-			x += 1UL << (frac_bits - 1);
-			x >>= frac_bits;
-		}
-	}
-
-	return result;
-}
-
-/*
- * a1 = a0 * e + a * (1 - e)
- *
- * a2 = a1 * e + a * (1 - e)
- *    = (a0 * e + a * (1 - e)) * e + a * (1 - e)
- *    = a0 * e^2 + a * (1 - e) * (1 + e)
- *
- * a3 = a2 * e + a * (1 - e)
- *    = (a0 * e^2 + a * (1 - e) * (1 + e)) * e + a * (1 - e)
- *    = a0 * e^3 + a * (1 - e) * (1 + e + e^2)
- *
- *  ...
- *
- * an = a0 * e^n + a * (1 - e) * (1 + e + ... + e^n-1) [1]
- *    = a0 * e^n + a * (1 - e) * (1 - e^n)/(1 - e)
- *    = a0 * e^n + a * (1 - e^n)
- *
- * [1] application of the geometric series:
- *
- *              n         1 - x^(n+1)
- *     S_n := \Sum x^i = -------------
- *             i=0          1 - x
- */
-static unsigned long
-calc_load_n(unsigned long load, unsigned long exp,
-	    unsigned long active, unsigned int n)
-{
-	return calc_load(load, fixed_power_int(exp, FSHIFT, n), active);
-}
-
 /*
  * NO_HZ can leave us missing all per-CPU ticks calling
  * calc_load_fold_active(), but since a NO_HZ CPU folds its delta into
-- 
2.18.0

[PATCH 6/9] sched: sched.h: make rq locking and clock functions available in stats.h

[Johannes Weiner]

kernel/sched/sched.h includes "stats.h" half-way through the file. The
next patch introduces users of sched.h's rq locking functions and
update_rq_clock() in kernel/sched/stats.h. Move those definitions up
in the file so they are available in stats.h.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 kernel/sched/sched.h | 164 +++++++++++++++++++++----------------------
 1 file changed, 82 insertions(+), 82 deletions(-)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index cb467c221b15..b8f038497240 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -919,6 +919,8 @@ DECLARE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
 #define cpu_curr(cpu)		(cpu_rq(cpu)->curr)
 #define raw_rq()		raw_cpu_ptr(&runqueues)
 
+extern void update_rq_clock(struct rq *rq);
+
 static inline u64 __rq_clock_broken(struct rq *rq)
 {
 	return READ_ONCE(rq->clock);
@@ -1037,6 +1039,86 @@ static inline void rq_repin_lock(struct rq *rq, struct rq_flags *rf)
 #endif
 }
 
+struct rq *__task_rq_lock(struct task_struct *p, struct rq_flags *rf)
+	__acquires(rq->lock);
+
+struct rq *task_rq_lock(struct task_struct *p, struct rq_flags *rf)
+	__acquires(p->pi_lock)
+	__acquires(rq->lock);
+
+static inline void __task_rq_unlock(struct rq *rq, struct rq_flags *rf)
+	__releases(rq->lock)
+{
+	rq_unpin_lock(rq, rf);
+	raw_spin_unlock(&rq->lock);
+}
+
+static inline void
+task_rq_unlock(struct rq *rq, struct task_struct *p, struct rq_flags *rf)
+	__releases(rq->lock)
+	__releases(p->pi_lock)
+{
+	rq_unpin_lock(rq, rf);
+	raw_spin_unlock(&rq->lock);
+	raw_spin_unlock_irqrestore(&p->pi_lock, rf->flags);
+}
+
+static inline void
+rq_lock_irqsave(struct rq *rq, struct rq_flags *rf)
+	__acquires(rq->lock)
+{
+	raw_spin_lock_irqsave(&rq->lock, rf->flags);
+	rq_pin_lock(rq, rf);
+}
+
+static inline void
+rq_lock_irq(struct rq *rq, struct rq_flags *rf)
+	__acquires(rq->lock)
+{
+	raw_spin_lock_irq(&rq->lock);
+	rq_pin_lock(rq, rf);
+}
+
+static inline void
+rq_lock(struct rq *rq, struct rq_flags *rf)
+	__acquires(rq->lock)
+{
+	raw_spin_lock(&rq->lock);
+	rq_pin_lock(rq, rf);
+}
+
+static inline void
+rq_relock(struct rq *rq, struct rq_flags *rf)
+	__acquires(rq->lock)
+{
+	raw_spin_lock(&rq->lock);
+	rq_repin_lock(rq, rf);
+}
+
+static inline void
+rq_unlock_irqrestore(struct rq *rq, struct rq_flags *rf)
+	__releases(rq->lock)
+{
+	rq_unpin_lock(rq, rf);
+	raw_spin_unlock_irqrestore(&rq->lock, rf->flags);
+}
+
+static inline void
+rq_unlock_irq(struct rq *rq, struct rq_flags *rf)
+	__releases(rq->lock)
+{
+	rq_unpin_lock(rq, rf);
+	raw_spin_unlock_irq(&rq->lock);
+}
+
+static inline void
+rq_unlock(struct rq *rq, struct rq_flags *rf)
+	__releases(rq->lock)
+{
+	rq_unpin_lock(rq, rf);
+	raw_spin_unlock(&rq->lock);
+}
+
 #ifdef CONFIG_NUMA
 enum numa_topology_type {
 	NUMA_DIRECT,
@@ -1670,8 +1752,6 @@ static inline void sub_nr_running(struct rq *rq, unsigned count)
 	sched_update_tick_dependency(rq);
 }
 
-extern void update_rq_clock(struct rq *rq);
-
 extern void activate_task(struct rq *rq, struct task_struct *p, int flags);
 extern void deactivate_task(struct rq *rq, struct task_struct *p, int flags);
 
@@ -1752,86 +1832,6 @@ static inline void sched_rt_avg_update(struct rq *rq, u64 rt_delta) { }
 static inline void sched_avg_update(struct rq *rq) { }
 #endif
 
-struct rq *__task_rq_lock(struct task_struct *p, struct rq_flags *rf)
-	__acquires(rq->lock);
-
-struct rq *task_rq_lock(struct task_struct *p, struct rq_flags *rf)
-	__acquires(p->pi_lock)
-	__acquires(rq->lock);
-
-static inline void __task_rq_unlock(struct rq *rq, struct rq_flags *rf)
-	__releases(rq->lock)
-{
-	rq_unpin_lock(rq, rf);
-	raw_spin_unlock(&rq->lock);
-}
-
-static inline void
-task_rq_unlock(struct rq *rq, struct task_struct *p, struct rq_flags *rf)
-	__releases(rq->lock)
-	__releases(p->pi_lock)
-{
-	rq_unpin_lock(rq, rf);
-	raw_spin_unlock(&rq->lock);
-	raw_spin_unlock_irqrestore(&p->pi_lock, rf->flags);
-}
-
-static inline void
-rq_lock_irqsave(struct rq *rq, struct rq_flags *rf)
-	__acquires(rq->lock)
-{
-	raw_spin_lock_irqsave(&rq->lock, rf->flags);
-	rq_pin_lock(rq, rf);
-}
-
-static inline void
-rq_lock_irq(struct rq *rq, struct rq_flags *rf)
-	__acquires(rq->lock)
-{
-	raw_spin_lock_irq(&rq->lock);
-	rq_pin_lock(rq, rf);
-}
-
-static inline void
-rq_lock(struct rq *rq, struct rq_flags *rf)
-	__acquires(rq->lock)
-{
-	raw_spin_lock(&rq->lock);
-	rq_pin_lock(rq, rf);
-}
-
-static inline void
-rq_relock(struct rq *rq, struct rq_flags *rf)
-	__acquires(rq->lock)
-{
-	raw_spin_lock(&rq->lock);
-	rq_repin_lock(rq, rf);
-}
-
-static inline void
-rq_unlock_irqrestore(struct rq *rq, struct rq_flags *rf)
-	__releases(rq->lock)
-{
-	rq_unpin_lock(rq, rf);
-	raw_spin_unlock_irqrestore(&rq->lock, rf->flags);
-}
-
-static inline void
-rq_unlock_irq(struct rq *rq, struct rq_flags *rf)
-	__releases(rq->lock)
-{
-	rq_unpin_lock(rq, rf);
-	raw_spin_unlock_irq(&rq->lock);
-}
-
-static inline void
-rq_unlock(struct rq *rq, struct rq_flags *rf)
-	__releases(rq->lock)
-{
-	rq_unpin_lock(rq, rf);
-	raw_spin_unlock(&rq->lock);
-}
-
 #ifdef CONFIG_SMP
 #ifdef CONFIG_PREEMPT
 
-- 
2.18.0

[PATCH 7/9] sched: introduce this_rq_lock_irq()

[Johannes Weiner]

do_sched_yield() disables IRQs, looks up this_rq() and locks it. The
next patch is adding another site with the same pattern, so provide a
convenience function for it.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 kernel/sched/core.c  |  4 +---
 kernel/sched/sched.h | 12 ++++++++++++
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 211890edf37e..9586a8141f16 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4960,9 +4960,7 @@ static void do_sched_yield(void)
 	struct rq_flags rf;
 	struct rq *rq;
 
-	local_irq_disable();
-	rq = this_rq();
-	rq_lock(rq, &rf);
+	rq = this_rq_lock_irq(&rf);
 
 	schedstat_inc(rq->yld_count);
 	current->sched_class->yield_task(rq);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index b8f038497240..bc798c7cb4d4 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1119,6 +1119,18 @@ rq_unlock(struct rq *rq, struct rq_flags *rf)
 	raw_spin_unlock(&rq->lock);
 }
 
+static inline struct rq *
+this_rq_lock_irq(struct rq_flags *rf)
+	__acquires(rq->lock)
+{
+	struct rq *rq;
+
+	local_irq_disable();
+	rq = this_rq();
+	rq_lock(rq, rf);
+	return rq;
+}
+
 #ifdef CONFIG_NUMA
 enum numa_topology_type {
 	NUMA_DIRECT,
-- 
2.18.0

[PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

[Johannes Weiner]

When systems are overcommitted and resources become contended, it's
hard to tell exactly the impact this has on workload productivity, or
how close the system is to lockups and OOM kills. In particular, when
machines work multiple jobs concurrently, the impact of overcommit in
terms of latency and throughput on the individual job can be enormous.

In order to maximize hardware utilization without sacrificing
individual job health or risk complete machine lockups, this patch
implements a way to quantify resource pressure in the system.

A kernel built with CONFIG_PSI=y creates files in /proc/pressure/ that
expose the percentage of time the system is stalled on CPU, memory, or
IO, respectively. Stall states are aggregate versions of the per-task
delay accounting delays:

       cpu: some tasks are runnable but not executing on a CPU
       memory: tasks are reclaiming, or waiting for swapin or thrashing cache
       io: tasks are waiting for io completions

These percentages of walltime can be thought of as pressure
percentages, and they give a general sense of system health and
productivity loss incurred by resource overcommit. They can also
indicate when the system is approaching lockup scenarios and OOMs.

To do this, psi keeps track of the task states associated with each
CPU and samples the time they spend in stall states. Every 2 seconds,
the samples are averaged across CPUs - weighted by the CPUs' non-idle
time to eliminate artifacts from unused CPUs - and translated into
percentages of walltime. A running average of those percentages is
maintained over 10s, 1m, and 5m periods (similar to the loadaverage).

v2:
- stable clock tick, as per Peter
- data structure layout optimization, as per Peter
- fix u64 divisions on 32 bit, as per Peter
- outermost psi_disabled checks, as per Peter
- coding style fixes, as per Peter
- just-in-time stats aggregation, as per Suren
- fix task state corruption with CONFIG_PREEMPT, as per Suren
- CONFIG_PSI=n build error
- avoid writing p->sched_psi_wake_requeue unnecessarily
- documentation & comment updates

v3:
- pack scheduler hotpath data into one cacheline, as per Peter and Linus
- drop unnecessary SCHED_INFO dependency, as per Peter
- lockless live-state aggregation, as per Peter
- do_div -> div64_ul and some other cleanups, as per Peter
- realtime sampling period and slipped sample handling, as per Tejun

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 Documentation/accounting/psi.txt |  64 +++
 include/linux/psi.h              |  27 ++
 include/linux/psi_types.h        |  87 +++++
 include/linux/sched.h            |  10 +
 init/Kconfig                     |  15 +
 kernel/fork.c                    |   4 +
 kernel/sched/Makefile            |   1 +
 kernel/sched/core.c              |  11 +-
 kernel/sched/psi.c               | 643 +++++++++++++++++++++++++++++++
 kernel/sched/sched.h             |   2 +
 kernel/sched/stats.h             |  80 ++++
 mm/compaction.c                  |   5 +
 mm/filemap.c                     |  15 +-
 mm/page_alloc.c                  |  10 +
 mm/vmscan.c                      |  13 +
 15 files changed, 981 insertions(+), 6 deletions(-)
 create mode 100644 Documentation/accounting/psi.txt
 create mode 100644 include/linux/psi.h
 create mode 100644 include/linux/psi_types.h
 create mode 100644 kernel/sched/psi.c

diff --git a/Documentation/accounting/psi.txt b/Documentation/accounting/psi.txt
new file mode 100644
index 000000000000..51e7ef14142e
--- /dev/null
+++ b/Documentation/accounting/psi.txt
@@ -0,0 +1,64 @@
+================================
+PSI - Pressure Stall Information
+================================
+
+:Date: April, 2018
+:Author: Johannes Weiner <hannes@cmpxchg.org>
+
+When CPU, memory or IO devices are contended, workloads experience
+latency spikes, throughput losses, and run the risk of OOM kills.
+
+Without an accurate measure of such contention, users are forced to
+either play it safe and under-utilize their hardware resources, or
+roll the dice and frequently suffer the disruptions resulting from
+excessive overcommit.
+
+The psi feature identifies and quantifies the disruptions caused by
+such resource crunches and the time impact it has on complex workloads
+or even entire systems.
+
+Having an accurate measure of productivity losses caused by resource
+scarcity aids users in sizing workloads to hardware--or provisioning
+hardware according to workload demand.
+
+As psi aggregates this information in realtime, systems can be managed
+dynamically using techniques such as load shedding, migrating jobs to
+other systems or data centers, or strategically pausing or killing low
+priority or restartable batch jobs.
+
+This allows maximizing hardware utilization without sacrificing
+workload health or risking major disruptions such as OOM kills.
+
+Pressure interface
+==================
+
+Pressure information for each resource is exported through the
+respective file in /proc/pressure/ -- cpu, memory, and io.
+
+In both cases, the format for CPU is as such:
+
+some avg10=0.00 avg60=0.00 avg300=0.00 total=0
+
+and for memory and IO:
+
+some avg10=0.00 avg60=0.00 avg300=0.00 total=0
+full avg10=0.00 avg60=0.00 avg300=0.00 total=0
+
+The "some" line indicates the share of time in which at least some
+tasks are stalled on a given resource.
+
+The "full" line indicates the share of time in which all non-idle
+tasks are stalled on a given resource simultaneously. In this state
+actual CPU cycles are going to waste, and a workload that spends
+extended time in this state is considered to be thrashing. This has
+severe impact on performance, and it's useful to distinguish this
+situation from a state where some tasks are stalled but the CPU is
+still doing productive work. As such, time spent in this subset of the
+stall state is tracked separately and exported in the "full" averages.
+
+The ratios are tracked as recent trends over ten, sixty, and three
+hundred second windows, which gives insight into short term events as
+well as medium and long term trends. The total absolute stall time is
+tracked and exported as well, to allow detection of latency spikes
+which wouldn't necessarily make a dent in the time averages, or to
+average trends over custom time frames.
diff --git a/include/linux/psi.h b/include/linux/psi.h
new file mode 100644
index 000000000000..371af1479699
--- /dev/null
+++ b/include/linux/psi.h
@@ -0,0 +1,27 @@
+#ifndef _LINUX_PSI_H
+#define _LINUX_PSI_H
+
+#include <linux/psi_types.h>
+#include <linux/sched.h>
+
+#ifdef CONFIG_PSI
+
+extern bool psi_disabled;
+
+void psi_init(void);
+
+void psi_task_change(struct task_struct *task, u64 now, int clear, int set);
+
+void psi_memstall_enter(unsigned long *flags);
+void psi_memstall_leave(unsigned long *flags);
+
+#else /* CONFIG_PSI */
+
+static inline void psi_init(void) {}
+
+static inline void psi_memstall_enter(unsigned long *flags) {}
+static inline void psi_memstall_leave(unsigned long *flags) {}
+
+#endif /* CONFIG_PSI */
+
+#endif /* _LINUX_PSI_H */
diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
new file mode 100644
index 000000000000..b6ff46362eb3
--- /dev/null
+++ b/include/linux/psi_types.h
@@ -0,0 +1,87 @@
+#ifndef _LINUX_PSI_TYPES_H
+#define _LINUX_PSI_TYPES_H
+
+#include <linux/types.h>
+
+#ifdef CONFIG_PSI
+
+/* Tracked task states */
+enum psi_task_count {
+	NR_IOWAIT,
+	NR_MEMSTALL,
+	NR_RUNNING,
+	NR_PSI_TASK_COUNTS,
+};
+
+/* Task state bitmasks */
+#define TSK_IOWAIT	(1 << NR_IOWAIT)
+#define TSK_MEMSTALL	(1 << NR_MEMSTALL)
+#define TSK_RUNNING	(1 << NR_RUNNING)
+
+/* Resources that workloads could be stalled on */
+enum psi_res {
+	PSI_IO,
+	PSI_MEM,
+	PSI_CPU,
+	NR_PSI_RESOURCES,
+};
+
+/*
+ * Pressure states for each resource:
+ *
+ * SOME: Stalled tasks & working tasks
+ * FULL: Stalled tasks & no working tasks
+ */
+enum psi_states {
+	PSI_IO_SOME,
+	PSI_IO_FULL,
+	PSI_MEM_SOME,
+	PSI_MEM_FULL,
+	PSI_CPU_SOME,
+	PSI_NONIDLE,
+	NR_PSI_STATES,
+};
+
+struct psi_group_cpu {
+	/* 1st cacheline updated by the scheduler */
+
+	/* States of the tasks belonging to this group */
+	unsigned int tasks[NR_PSI_TASK_COUNTS] ____cacheline_aligned_in_smp;
+
+	/* Period time sampling buckets for each state of interest (ns) */
+	u32 times[NR_PSI_STATES];
+
+	/* Time of last task change in this group (rq_clock) */
+	u64 state_start;
+
+	/* 2nd cacheline updated by the aggregator */
+
+	/* Delta detection against the sampling buckets */
+	u32 times_prev[NR_PSI_STATES] ____cacheline_aligned_in_smp;
+};
+
+struct psi_group {
+	/* Protects data updated during an aggregation */
+	struct mutex stat_lock;
+
+	/* Per-cpu task state & time tracking */
+	struct psi_group_cpu __percpu *pcpu;
+
+	/* Periodic aggregation state */
+	u64 total_prev[NR_PSI_STATES - 1];
+	u64 last_update;
+	u64 next_update;
+	struct delayed_work clock_work;
+
+	/* Total stall times and sampled pressure averages */
+	u64 total[NR_PSI_STATES - 1];
+	unsigned long avg[NR_PSI_STATES - 1][3];
+};
+
+#else /* CONFIG_PSI */
+
+struct psi_group { };
+
+#endif /* CONFIG_PSI */
+
+#endif /* _LINUX_PSI_TYPES_H */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index ca3f3eae8980..d5e4ee234114 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -25,6 +25,7 @@
 #include <linux/latencytop.h>
 #include <linux/sched/prio.h>
 #include <linux/signal_types.h>
+#include <linux/psi_types.h>
 #include <linux/mm_types_task.h>
 #include <linux/task_io_accounting.h>
 
@@ -709,6 +710,10 @@ struct task_struct {
 	unsigned			sched_contributes_to_load:1;
 	unsigned			sched_migrated:1;
 	unsigned			sched_remote_wakeup:1;
+#ifdef CONFIG_PSI
+	unsigned			sched_psi_wake_requeue:1;
+#endif
+
 	/* Force alignment to the next boundary: */
 	unsigned			:0;
 
@@ -956,6 +961,10 @@ struct task_struct {
 	siginfo_t			*last_siginfo;
 
 	struct task_io_accounting	ioac;
+#ifdef CONFIG_PSI
+	/* Pressure stall state */
+	unsigned int			psi_flags;
+#endif
 #ifdef CONFIG_TASK_XACCT
 	/* Accumulated RSS usage: */
 	u64				acct_rss_mem1;
@@ -1385,6 +1394,7 @@ extern struct pid *cad_pid;
 #define PF_KTHREAD		0x00200000	/* I am a kernel thread */
 #define PF_RANDOMIZE		0x00400000	/* Randomize virtual address space */
 #define PF_SWAPWRITE		0x00800000	/* Allowed to write to swap */
+#define PF_MEMSTALL		0x01000000	/* Stalled due to lack of memory */
 #define PF_NO_SETAFFINITY	0x04000000	/* Userland is not allowed to meddle with cpus_allowed */
 #define PF_MCE_EARLY		0x08000000      /* Early kill for mce process policy */
 #define PF_MUTEX_TESTER		0x20000000	/* Thread belongs to the rt mutex tester */
diff --git a/init/Kconfig b/init/Kconfig
index 18b151f0ddc1..ad61ddb5d68e 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -457,6 +457,21 @@ config TASK_IO_ACCOUNTING
 
 	  Say N if unsure.
 
+config PSI
+	bool "Pressure stall information tracking"
+	help
+	  Collect metrics that indicate how overcommitted the CPU, memory,
+	  and IO capacity are in the system.
+
+	  If you say Y here, the kernel will create /proc/pressure/ with the
+	  pressure statistics files cpu, memory, and io. These will indicate
+	  the share of walltime in which some or all tasks in the system are
+	  delayed due to contention of the respective resource.
+
+	  For more details see Documentation/accounting/psi.txt.
+
+	  Say N if unsure.
+
 endmenu # "CPU/Task time and stats accounting"
 
 config CPU_ISOLATION
diff --git a/kernel/fork.c b/kernel/fork.c
index a5d21c42acfc..067aa5c28526 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1704,6 +1704,10 @@ static __latent_entropy struct task_struct *copy_process(
 
 	p->default_timer_slack_ns = current->timer_slack_ns;
 
+#ifdef CONFIG_PSI
+	p->psi_flags = 0;
+#endif
+
 	task_io_accounting_init(&p->ioac);
 	acct_clear_integrals(p);
 
diff --git a/kernel/sched/Makefile b/kernel/sched/Makefile
index d9a02b318108..b29bc18f2704 100644
--- a/kernel/sched/Makefile
+++ b/kernel/sched/Makefile
@@ -29,3 +29,4 @@ obj-$(CONFIG_CPU_FREQ) += cpufreq.o
 obj-$(CONFIG_CPU_FREQ_GOV_SCHEDUTIL) += cpufreq_schedutil.o
 obj-$(CONFIG_MEMBARRIER) += membarrier.o
 obj-$(CONFIG_CPU_ISOLATION) += isolation.o
+obj-$(CONFIG_PSI) += psi.o
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9586a8141f16..e53137df405b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -743,8 +743,10 @@ static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
 	if (!(flags & ENQUEUE_NOCLOCK))
 		update_rq_clock(rq);
 
-	if (!(flags & ENQUEUE_RESTORE))
+	if (!(flags & ENQUEUE_RESTORE)) {
 		sched_info_queued(rq, p);
+		psi_enqueue(rq, p, flags & ENQUEUE_WAKEUP);
+	}
 
 	p->sched_class->enqueue_task(rq, p, flags);
 }
@@ -754,8 +756,10 @@ static inline void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
 	if (!(flags & DEQUEUE_NOCLOCK))
 		update_rq_clock(rq);
 
-	if (!(flags & DEQUEUE_SAVE))
+	if (!(flags & DEQUEUE_SAVE)) {
 		sched_info_dequeued(rq, p);
+		psi_dequeue(rq, p, flags & DEQUEUE_SLEEP);
+	}
 
 	p->sched_class->dequeue_task(rq, p, flags);
 }
@@ -2058,6 +2062,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
 	cpu = select_task_rq(p, p->wake_cpu, SD_BALANCE_WAKE, wake_flags);
 	if (task_cpu(p) != cpu) {
 		wake_flags |= WF_MIGRATED;
+		psi_ttwu_dequeue(p);
 		set_task_cpu(p, cpu);
 	}
 
@@ -6124,6 +6129,8 @@ void __init sched_init(void)
 
 	init_schedstats();
 
+	psi_init();
+
 	scheduler_running = 1;
 }
 
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
new file mode 100644
index 000000000000..57ec86592b5a
--- /dev/null
+++ b/kernel/sched/psi.c
@@ -0,0 +1,643 @@
+/*
+ * Pressure stall information for CPU, memory and IO
+ *
+ * Copyright (c) 2018 Facebook, Inc.
+ * Author: Johannes Weiner <hannes@cmpxchg.org>
+ *
+ * When CPU, memory and IO are contended, tasks experience delays that
+ * reduce throughput and introduce latencies into the workload. Memory
+ * and IO contention, in addition, can cause a full loss of forward
+ * progress in which the CPU goes idle.
+ *
+ * This code aggregates individual task delays into resource pressure
+ * metrics that indicate problems with both workload health and
+ * resource utilization.
+ *
+ *			Model
+ *
+ * The time in which a task can execute on a CPU is our baseline for
+ * productivity. Pressure expresses the amount of time in which this
+ * potential cannot be realized due to resource contention.
+ *
+ * This concept of productivity has two components: the workload and
+ * the CPU. To measure the impact of pressure on both, we define two
+ * contention states for a resource: SOME and FULL.
+ *
+ * In the SOME state of a given resource, one or more tasks are
+ * delayed on that resource. This affects the workload's ability to
+ * perform work, but the CPU may still be executing other tasks.
+ *
+ * In the FULL state of a given resource, all non-idle tasks are
+ * delayed on that resource such that nobody is advancing and the CPU
+ * goes idle. This leaves both workload and CPU unproductive.
+ *
+ * (Naturally, the FULL state doesn't exist for the CPU resource.)
+ *
+ *	SOME = nr_delayed_tasks != 0
+ *	FULL = nr_delayed_tasks != 0 && nr_running_tasks == 0
+ *
+ * The percentage of wallclock time spent in those compound stall
+ * states gives pressure numbers between 0 and 100 for each resource,
+ * where the SOME percentage indicates workload slowdowns and the FULL
+ * percentage indicates reduced CPU utilization:
+ *
+ *	%SOME = time(SOME) / period
+ *	%FULL = time(FULL) / period
+ *
+ *			Multiple CPUs
+ *
+ * The more tasks and available CPUs there are, the more work can be
+ * performed concurrently. This means that the potential that can go
+ * unrealized due to resource contention *also* scales with non-idle
+ * tasks and CPUs.
+ *
+ * Consider a scenario where 257 number crunching tasks are trying to
+ * run concurrently on 256 CPUs. If we simply aggregated the task
+ * states, we would have to conclude a CPU SOME pressure number of
+ * 100%, since *somebody* is waiting on a runqueue at all
+ * times. However, that is clearly not the amount of contention the
+ * workload is experiencing: only one out of 256 possible exceution
+ * threads will be contended at any given time, or about 0.4%.
+ *
+ * Conversely, consider a scenario of 4 tasks and 4 CPUs where at any
+ * given time *one* of the tasks is delayed due to a lack of memory.
+ * Again, looking purely at the task state would yield a memory FULL
+ * pressure number of 0%, since *somebody* is always making forward
+ * progress. But again this wouldn't capture the amount of execution
+ * potential lost, which is 1 out of 4 CPUs, or 25%.
+ *
+ * To calculate wasted potential (pressure) with multiple processors,
+ * we have to base our calculation on the number of non-idle tasks in
+ * conjunction with the number of available CPUs, which is the number
+ * of potential execution threads. SOME becomes then the proportion of
+ * delayed tasks to possibe threads, and FULL is the share of possible
+ * threads that are unproductive due to delays:
+ *
+ *	threads = min(nr_nonidle_tasks, nr_cpus)
+ *	   SOME = min(nr_delayed_tasks / threads, 1)
+ *	   FULL = (threads - min(nr_running_tasks, threads)) / threads
+ *
+ * For the 257 number crunchers on 256 CPUs, this yields:
+ *
+ *	threads = min(257, 256)
+ *	   SOME = min(1 / 256, 1)             = 0.4%
+ *	   FULL = (256 - min(257, 256)) / 256 = 0%
+ *
+ * For the 1 out of 4 memory-delayed tasks, this yields:
+ *
+ *	threads = min(4, 4)
+ *	   SOME = min(1 / 4, 1)               = 25%
+ *	   FULL = (4 - min(3, 4)) / 4         = 25%
+ *
+ * [ Substitute nr_cpus with 1, and you can see that it's a natural
+ *   extension of the single-CPU model. ]
+ *
+ *			Implementation
+ *
+ * To assess the precise time spent in each such state, we would have
+ * to freeze the system on task changes and start/stop the state
+ * clocks accordingly. Obviously that doesn't scale in practice.
+ *
+ * Because the scheduler aims to distribute the compute load evenly
+ * among the available CPUs, we can track task state locally to each
+ * CPU and, at much lower frequency, extrapolate the global state for
+ * the cumulative stall times and the running averages.
+ *
+ * For each runqueue, we track:
+ *
+ *	   tSOME[cpu] = time(nr_delayed_tasks[cpu] != 0)
+ *	   tFULL[cpu] = time(nr_delayed_tasks[cpu] && !nr_running_tasks[cpu])
+ *	tNONIDLE[cpu] = time(nr_nonidle_tasks[cpu] != 0)
+ *
+ * and then periodically aggregate:
+ *
+ *	tNONIDLE = sum(tNONIDLE[i])
+ *
+ *	   tSOME = sum(tSOME[i] * tNONIDLE[i]) / tNONIDLE
+ *	   tFULL = sum(tFULL[i] * tNONIDLE[i]) / tNONIDLE
+ *
+ *	   %SOME = tSOME / period
+ *	   %FULL = tFULL / period
+ *
+ * This gives us an approximation of pressure that is practical
+ * cost-wise, yet way more sensitive and accurate than periodic
+ * sampling of the aggregate task states would be.
+ */
+
+#include <linux/sched/loadavg.h>
+#include <linux/seq_file.h>
+#include <linux/proc_fs.h>
+#include <linux/cgroup.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/psi.h>
+#include "sched.h"
+
+static int psi_bug __read_mostly;
+
+bool psi_disabled __read_mostly;
+core_param(psi_disabled, psi_disabled, bool, 0644);
+
+/* Running averages - we need to be higher-res than loadavg */
+#define PSI_FREQ	(2*HZ+1)	/* 2 sec intervals */
+#define EXP_10s		1677		/* 1/exp(2s/10s) as fixed-point */
+#define EXP_60s		1981		/* 1/exp(2s/60s) */
+#define EXP_300s	2034		/* 1/exp(2s/300s) */
+
+/* Sampling frequency in nanoseconds */
+static u64 psi_period __read_mostly;
+
+/* System-level pressure and stall tracking */
+static DEFINE_PER_CPU(struct psi_group_cpu, system_group_pcpu);
+static struct psi_group psi_system = {
+	.pcpu = &system_group_pcpu,
+};
+
+static void psi_clock(struct work_struct *work);
+
+static void psi_group_init(struct psi_group *group)
+{
+	group->next_update = sched_clock() + psi_period;
+	INIT_DELAYED_WORK(&group->clock_work, psi_clock);
+	mutex_init(&group->stat_lock);
+}
+
+void __init psi_init(void)
+{
+	if (psi_disabled)
+		return;
+
+	psi_period = jiffies_to_nsecs(PSI_FREQ);
+	psi_group_init(&psi_system);
+}
+
+static void calc_avgs(unsigned long avg[3], int missed_periods,
+		      u64 time, u64 period)
+{
+	unsigned long pct;
+
+	/* Fill in zeroes for periods of no activity */
+	if (missed_periods) {
+		avg[0] = calc_load_n(avg[0], EXP_10s, 0, missed_periods);
+		avg[1] = calc_load_n(avg[1], EXP_60s, 0, missed_periods);
+		avg[2] = calc_load_n(avg[2], EXP_300s, 0, missed_periods);
+	}
+
+	/* Sample the most recent active period */
+	pct = div_u64(time * 100, period);
+	pct *= FIXED_1;
+	avg[0] = calc_load(avg[0], EXP_10s, pct);
+	avg[1] = calc_load(avg[1], EXP_60s, pct);
+	avg[2] = calc_load(avg[2], EXP_300s, pct);
+}
+
+static bool test_state(unsigned int *tasks, int cpu, enum psi_states state)
+{
+	switch (state) {
+	case PSI_IO_SOME:
+		return tasks[NR_IOWAIT];
+	case PSI_IO_FULL:
+		return tasks[NR_IOWAIT] && !tasks[NR_RUNNING];
+	case PSI_MEM_SOME:
+		return tasks[NR_MEMSTALL];
+	case PSI_MEM_FULL:
+		/*
+		 * Since we care about lost potential, things are
+		 * fully blocked on memory when there are no other
+		 * working tasks, but also when the CPU is actively
+		 * being used by a reclaimer and nothing productive
+		 * could run even if it were runnable.
+		 */
+		return tasks[NR_MEMSTALL] &&
+			(!tasks[NR_RUNNING] ||
+			 cpu_curr(cpu)->flags & PF_MEMSTALL);
+	case PSI_CPU_SOME:
+		return tasks[NR_RUNNING] > 1;
+	case PSI_NONIDLE:
+		return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] ||
+			tasks[NR_RUNNING];
+	default:
+		return false;
+	}
+}
+
+static bool psi_update_stats(struct psi_group *group)
+{
+	u64 deltas[NR_PSI_STATES - 1] = { 0, };
+	unsigned long missed_periods = 0;
+	unsigned long nonidle_total = 0;
+	u64 now, expires, period;
+	int cpu;
+	int s;
+
+	mutex_lock(&group->stat_lock);
+
+	/*
+	 * Collect the per-cpu time buckets and average them into a
+	 * single time sample that is normalized to wallclock time.
+	 *
+	 * For averaging, each CPU is weighted by its non-idle time in
+	 * the sampling period. This eliminates artifacts from uneven
+	 * loading, or even entirely idle CPUs.
+	 *
+	 * We don't need to synchronize against CPU hotplugging. If we
+	 * see a CPU that's online and has samples, we incorporate it.
+	 */
+	for_each_online_cpu(cpu) {
+		struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu);
+		u32 uninitialized_var(nonidle);
+
+		BUILD_BUG_ON(PSI_NONIDLE != NR_PSI_STATES - 1);
+
+		for (s = PSI_NONIDLE; s >= 0; s--) {
+			u32 time, delta;
+
+			time = READ_ONCE(groupc->times[s]);
+			/*
+			 * In addition to already concluded states, we
+			 * also incorporate currently active states on
+			 * the CPU, since states may last for many
+			 * sampling periods.
+			 *
+			 * This way we keep our delta sampling buckets
+			 * small (u32) and our reported pressure close
+			 * to what's actually happening.
+			 */
+			if (test_state(groupc->tasks, cpu, s)) {
+				/*
+				 * We can race with a state change and
+				 * need to make sure the state_start
+				 * update is ordered against the
+				 * updates to the live state and the
+				 * time buckets (groupc->times).
+				 *
+				 * 1. If we observe task state that
+				 * needs to be recorded, make sure we
+				 * see state_start from when that
+				 * state went into effect or we'll
+				 * count time from the previous state.
+				 *
+				 * 2. If the time delta has already
+				 * been added to the bucket, make sure
+				 * we don't see it in state_start or
+				 * we'll count it twice.
+				 *
+				 * If the time delta is out of
+				 * state_start but not in the time
+				 * bucket yet, we'll miss it entirely
+				 * and handle it in the next period.
+				 */
+				smp_rmb();
+				time += cpu_clock(cpu) - groupc->state_start;
+			}
+			delta = time - groupc->times_prev[s];
+			groupc->times_prev[s] = time;
+
+			if (s == PSI_NONIDLE) {
+				nonidle = nsecs_to_jiffies(delta);
+				nonidle_total += nonidle;
+			} else {
+				deltas[s] += (u64)delta * nonidle;
+			}
+		}
+	}
+
+	/*
+	 * Integrate the sample into the running statistics that are
+	 * reported to userspace: the cumulative stall times and the
+	 * decaying averages.
+	 *
+	 * Pressure percentages are sampled at PSI_FREQ. We might be
+	 * called more often when the user polls more frequently than
+	 * that; we might be called less often when there is no task
+	 * activity, thus no data, and clock ticks are sporadic. The
+	 * below handles both.
+	 */
+
+	/* total= */
+	for (s = 0; s < NR_PSI_STATES - 1; s++)
+		group->total[s] += div_u64(deltas[s], max(nonidle_total, 1UL));
+
+	/* avgX= */
+	now = sched_clock();
+	expires = group->next_update;
+	if (now < expires)
+		goto out;
+	if (now - expires > psi_period)
+		missed_periods = div_u64(now - expires, psi_period);
+
+	/*
+	 * The periodic clock tick can get delayed for various
+	 * reasons, especially on loaded systems. To avoid clock
+	 * drift, we schedule the clock in fixed psi_period intervals.
+	 * But the deltas we sample out of the per-cpu buckets above
+	 * are based on the actual time elapsing between clock ticks.
+	 */
+	group->next_update = expires + ((1 + missed_periods) * psi_period);
+	period = now - (group->last_update + (missed_periods * psi_period));
+	group->last_update = now;
+
+	for (s = 0; s < NR_PSI_STATES - 1; s++) {
+		u32 sample;
+
+		sample = group->total[s] - group->total_prev[s];
+		/*
+		 * Due to the lockless sampling of the time buckets,
+		 * recorded time deltas can slip into the next period,
+		 * which under full pressure can result in samples in
+		 * excess of the period length.
+		 *
+		 * We don't want to report non-sensical pressures in
+		 * excess of 100%, nor do we want to drop such events
+		 * on the floor. Instead we punt any overage into the
+		 * future until pressure subsides. By doing this we
+		 * don't underreport the occurring pressure curve, we
+		 * just report it delayed by one period length.
+		 *
+		 * The error isn't cumulative. As soon as another
+		 * delta slips from a period P to P+1, by definition
+		 * it frees up its time T in P.
+		 */
+		if (sample > period)
+			sample = period;
+		group->total_prev[s] += sample;
+		calc_avgs(group->avg[s], missed_periods, sample, period);
+	}
+out:
+	mutex_unlock(&group->stat_lock);
+	return nonidle_total;
+}
+
+static void psi_clock(struct work_struct *work)
+{
+	struct delayed_work *dwork;
+	struct psi_group *group;
+	bool nonidle;
+
+	dwork = to_delayed_work(work);
+	group = container_of(dwork, struct psi_group, clock_work);
+
+	/*
+	 * If there is task activity, periodically fold the per-cpu
+	 * times and feed samples into the running averages. If things
+	 * are idle and there is no data to process, stop the clock.
+	 * Once restarted, we'll catch up the running averages in one
+	 * go - see calc_avgs() and missed_periods.
+	 */
+
+	nonidle = psi_update_stats(group);
+
+	if (nonidle) {
+		unsigned long delay = 0;
+		u64 now;
+
+		now = sched_clock();
+		if (group->next_update > now)
+			delay = nsecs_to_jiffies(group->next_update - now) + 1;
+		schedule_delayed_work(dwork, delay);
+	}
+}
+
+static void psi_group_change(struct psi_group *group, int cpu, u64 now,
+			     unsigned int clear, unsigned int set)
+{
+	struct psi_group_cpu *groupc;
+	unsigned int t, m;
+	u32 delta;
+
+	groupc = per_cpu_ptr(group->pcpu, cpu);
+
+	/*
+	 * First we assess the aggregate resource states these CPU's
+	 * tasks have been in since the last change, and account any
+	 * SOME and FULL time that may have resulted in.
+	 *
+	 * Then we update the task counts according to the state
+	 * change requested through the @clear and @set bits.
+	 */
+
+	delta = now - groupc->state_start;
+	groupc->state_start = now;
+
+	/*
+	 * Update state_start before recording time in the sampling
+	 * buckets and changing task counts, to prevent a racing
+	 * aggregation from counting the delta twice or attributing it
+	 * to an old state.
+	 */
+	smp_wmb();
+
+	if (test_state(groupc->tasks, cpu, PSI_IO_SOME)) {
+		groupc->times[PSI_IO_SOME] += delta;
+		if (test_state(groupc->tasks, cpu, PSI_IO_FULL))
+			groupc->times[PSI_IO_FULL] += delta;
+	}
+	if (test_state(groupc->tasks, cpu, PSI_MEM_SOME)) {
+		groupc->times[PSI_MEM_SOME] += delta;
+		if (test_state(groupc->tasks, cpu, PSI_MEM_FULL))
+			groupc->times[PSI_MEM_FULL] += delta;
+	}
+	if (test_state(groupc->tasks, cpu, PSI_CPU_SOME))
+		groupc->times[PSI_CPU_SOME] += delta;
+	if (test_state(groupc->tasks, cpu, PSI_NONIDLE))
+		groupc->times[PSI_NONIDLE] += delta;
+
+	for (t = 0, m = clear; m; m &= ~(1 << t), t++) {
+		if (!(m & (1 << t)))
+			continue;
+		if (groupc->tasks[t] == 0 && !psi_bug) {
+			printk_deferred(KERN_ERR "psi: task underflow! cpu=%d t=%d tasks=[%u %u %u] clear=%x set=%x\n",
+					cpu, t, groupc->tasks[0],
+					groupc->tasks[1], groupc->tasks[2],
+					clear, set);
+			psi_bug = 1;
+		}
+		groupc->tasks[t]--;
+	}
+	for (t = 0; set; set &= ~(1 << t), t++)
+		if (set & (1 << t))
+			groupc->tasks[t]++;
+
+	if (!delayed_work_pending(&group->clock_work))
+		schedule_delayed_work(&group->clock_work, PSI_FREQ);
+}
+
+void psi_task_change(struct task_struct *task, u64 now, int clear, int set)
+{
+	int cpu = task_cpu(task);
+
+	if (psi_disabled)
+		return;
+
+	if (!task->pid)
+		return;
+
+	if (((task->psi_flags & set) ||
+	     (task->psi_flags & clear) != clear) &&
+	    !psi_bug) {
+		printk_deferred(KERN_ERR "psi: inconsistent task state! task=%d:%s cpu=%d psi_flags=%x clear=%x set=%x\n",
+				task->pid, task->comm, cpu,
+				task->psi_flags, clear, set);
+		psi_bug = 1;
+	}
+
+	task->psi_flags &= ~clear;
+	task->psi_flags |= set;
+
+	psi_group_change(&psi_system, cpu, now, clear, set);
+}
+
+/**
+ * psi_memstall_enter - mark the beginning of a memory stall section
+ * @flags: flags to handle nested sections
+ *
+ * Marks the calling task as being stalled due to a lack of memory,
+ * such as waiting for a refault or performing reclaim.
+ */
+void psi_memstall_enter(unsigned long *flags)
+{
+	struct rq_flags rf;
+	struct rq *rq;
+
+	if (psi_disabled)
+		return;
+
+	*flags = current->flags & PF_MEMSTALL;
+	if (*flags)
+		return;
+	/*
+	 * PF_MEMSTALL setting & accounting needs to be atomic wrt
+	 * changes to the task's scheduling state, otherwise we can
+	 * race with CPU migration.
+	 */
+	rq = this_rq_lock_irq(&rf);
+
+	update_rq_clock(rq);
+
+	current->flags |= PF_MEMSTALL;
+	psi_task_change(current, rq_clock(rq), 0, TSK_MEMSTALL);
+
+	rq_unlock_irq(rq, &rf);
+}
+
+/**
+ * psi_memstall_leave - mark the end of an memory stall section
+ * @flags: flags to handle nested memdelay sections
+ *
+ * Marks the calling task as no longer stalled due to lack of memory.
+ */
+void psi_memstall_leave(unsigned long *flags)
+{
+	struct rq_flags rf;
+	struct rq *rq;
+
+	if (psi_disabled)
+		return;
+
+	if (*flags)
+		return;
+	/*
+	 * PF_MEMSTALL clearing & accounting needs to be atomic wrt
+	 * changes to the task's scheduling state, otherwise we could
+	 * race with CPU migration.
+	 */
+	rq = this_rq_lock_irq(&rf);
+
+	update_rq_clock(rq);
+
+	current->flags &= ~PF_MEMSTALL;
+	psi_task_change(current, rq_clock(rq), TSK_MEMSTALL, 0);
+
+	rq_unlock_irq(rq, &rf);
+}
+
+static int psi_show(struct seq_file *m, struct psi_group *group,
+		    enum psi_res res)
+{
+	int full;
+
+	if (psi_disabled)
+		return -EOPNOTSUPP;
+
+	psi_update_stats(group);
+
+	for (full = 0; full < 2 - (res == PSI_CPU); full++) {
+		unsigned long avg[3];
+		u64 total;
+		int w;
+
+		for (w = 0; w < 3; w++)
+			avg[w] = group->avg[res * 2 + full][w];
+		total = div_u64(group->total[res * 2 + full], NSEC_PER_USEC);
+
+		seq_printf(m, "%s avg10=%lu.%02lu avg60=%lu.%02lu avg300=%lu.%02lu total=%llu\n",
+			   full ? "full" : "some",
+			   LOAD_INT(avg[0]), LOAD_FRAC(avg[0]),
+			   LOAD_INT(avg[1]), LOAD_FRAC(avg[1]),
+			   LOAD_INT(avg[2]), LOAD_FRAC(avg[2]),
+			   total);
+	}
+
+	return 0;
+}
+
+static int psi_io_show(struct seq_file *m, void *v)
+{
+	return psi_show(m, &psi_system, PSI_IO);
+}
+
+static int psi_memory_show(struct seq_file *m, void *v)
+{
+	return psi_show(m, &psi_system, PSI_MEM);
+}
+
+static int psi_cpu_show(struct seq_file *m, void *v)
+{
+	return psi_show(m, &psi_system, PSI_CPU);
+}
+
+static int psi_io_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, psi_io_show, NULL);
+}
+
+static int psi_memory_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, psi_memory_show, NULL);
+}
+
+static int psi_cpu_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, psi_cpu_show, NULL);
+}
+
+static const struct file_operations psi_io_fops = {
+	.open           = psi_io_open,
+	.read           = seq_read,
+	.llseek         = seq_lseek,
+	.release        = single_release,
+};
+
+static const struct file_operations psi_memory_fops = {
+	.open           = psi_memory_open,
+	.read           = seq_read,
+	.llseek         = seq_lseek,
+	.release        = single_release,
+};
+
+static const struct file_operations psi_cpu_fops = {
+	.open           = psi_cpu_open,
+	.read           = seq_read,
+	.llseek         = seq_lseek,
+	.release        = single_release,
+};
+
+static int __init psi_proc_init(void)
+{
+	proc_mkdir("pressure", NULL);
+	proc_create("pressure/io", 0, NULL, &psi_io_fops);
+	proc_create("pressure/memory", 0, NULL, &psi_memory_fops);
+	proc_create("pressure/cpu", 0, NULL, &psi_cpu_fops);
+	return 0;
+}
+module_init(psi_proc_init);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index bc798c7cb4d4..e798491ff329 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -54,6 +54,7 @@
 #include <linux/proc_fs.h>
 #include <linux/prefetch.h>
 #include <linux/profile.h>
+#include <linux/psi.h>
 #include <linux/rcupdate_wait.h>
 #include <linux/security.h>
 #include <linux/stackprotector.h>
@@ -320,6 +321,7 @@ extern bool dl_cpu_busy(unsigned int cpu);
 #ifdef CONFIG_CGROUP_SCHED
 
 #include <linux/cgroup.h>
+#include <linux/psi.h>
 
 struct cfs_rq;
 struct rt_rq;
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index 8aea199a39b4..f3e0267eb47d 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -55,6 +55,86 @@ static inline void rq_sched_info_depart  (struct rq *rq, unsigned long long delt
 # define   schedstat_val_or_zero(var)	0
 #endif /* CONFIG_SCHEDSTATS */
 
+#ifdef CONFIG_PSI
+/*
+ * PSI tracks state that persists across sleeps, such as iowaits and
+ * memory stalls. As a result, it has to distinguish between sleeps,
+ * where a task's runnable state changes, and requeues, where a task
+ * and its state are being moved between CPUs and runqueues.
+ */
+static inline void psi_enqueue(struct rq *rq, struct task_struct *p,
+			       bool wakeup)
+{
+	int clear = 0, set = TSK_RUNNING;
+
+	if (psi_disabled)
+		return;
+
+	if (!wakeup || p->sched_psi_wake_requeue) {
+		if (p->flags & PF_MEMSTALL)
+			set |= TSK_MEMSTALL;
+		if (p->sched_psi_wake_requeue)
+			p->sched_psi_wake_requeue = 0;
+	} else {
+		if (p->in_iowait)
+			clear |= TSK_IOWAIT;
+	}
+
+	psi_task_change(p, rq_clock(rq), clear, set);
+}
+
+static inline void psi_dequeue(struct rq *rq, struct task_struct *p, bool sleep)
+{
+	int clear = TSK_RUNNING, set = 0;
+
+	if (psi_disabled)
+		return;
+
+	if (!sleep) {
+		if (p->flags & PF_MEMSTALL)
+			clear |= TSK_MEMSTALL;
+	} else {
+		if (p->in_iowait)
+			set |= TSK_IOWAIT;
+	}
+
+	psi_task_change(p, rq_clock(rq), clear, set);
+}
+
+static inline void psi_ttwu_dequeue(struct task_struct *p)
+{
+	if (psi_disabled)
+		return;
+	/*
+	 * Is the task being migrated during a wakeup? Make sure to
+	 * deregister its sleep-persistent psi states from the old
+	 * queue, and let psi_enqueue() know it has to requeue.
+	 */
+	if (unlikely(p->in_iowait || (p->flags & PF_MEMSTALL))) {
+		struct rq_flags rf;
+		struct rq *rq;
+		int clear = 0;
+
+		if (p->in_iowait)
+			clear |= TSK_IOWAIT;
+		if (p->flags & PF_MEMSTALL)
+			clear |= TSK_MEMSTALL;
+
+		rq = __task_rq_lock(p, &rf);
+		update_rq_clock(rq);
+		psi_task_change(p, rq_clock(rq), clear, 0);
+		p->sched_psi_wake_requeue = 1;
+		__task_rq_unlock(rq, &rf);
+	}
+}
+#else /* CONFIG_PSI */
+static inline void psi_enqueue(struct rq *rq, struct task_struct *p,
+			       bool wakeup) {}
+static inline void psi_dequeue(struct rq *rq, struct task_struct *p,
+			       bool sleep) {}
+static inline void psi_ttwu_dequeue(struct task_struct *p) {}
+#endif /* CONFIG_PSI */
+
 #ifdef CONFIG_SCHED_INFO
 static inline void sched_info_reset_dequeued(struct task_struct *t)
 {
diff --git a/mm/compaction.c b/mm/compaction.c
index 29bd1df18b98..8f9566745902 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -22,6 +22,7 @@
 #include <linux/kthread.h>
 #include <linux/freezer.h>
 #include <linux/page_owner.h>
+#include <linux/psi.h>
 #include "internal.h"
 
 #ifdef CONFIG_COMPACTION
@@ -2068,11 +2069,15 @@ static int kcompactd(void *p)
 	pgdat->kcompactd_classzone_idx = pgdat->nr_zones - 1;
 
 	while (!kthread_should_stop()) {
+		unsigned long pflags;
+
 		trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
 		wait_event_freezable(pgdat->kcompactd_wait,
 				kcompactd_work_requested(pgdat));
 
+		psi_memstall_enter(&pflags);
 		kcompactd_do_work(pgdat);
+		psi_memstall_leave(&pflags);
 	}
 
 	return 0;
diff --git a/mm/filemap.c b/mm/filemap.c
index e49961e13dd9..eee06145b997 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -37,6 +37,7 @@
 #include <linux/shmem_fs.h>
 #include <linux/rmap.h>
 #include <linux/delayacct.h>
+#include <linux/psi.h>
 #include "internal.h"
 
 #define CREATE_TRACE_POINTS
@@ -1075,11 +1076,14 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 	struct wait_page_queue wait_page;
 	wait_queue_entry_t *wait = &wait_page.wait;
 	bool thrashing = false;
+	unsigned long pflags;
 	int ret = 0;
 
-	if (bit_nr == PG_locked && !PageSwapBacked(page) &&
+	if (bit_nr == PG_locked &&
 	    !PageUptodate(page) && PageWorkingset(page)) {
-		delayacct_thrashing_start();
+		if (!PageSwapBacked(page))
+			delayacct_thrashing_start();
+		psi_memstall_enter(&pflags);
 		thrashing = true;
 	}
 
@@ -1121,8 +1125,11 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 
 	finish_wait(q, wait);
 
-	if (thrashing)
-		delayacct_thrashing_end();
+	if (thrashing) {
+		if (!PageSwapBacked(page))
+			delayacct_thrashing_end();
+		psi_memstall_leave(&pflags);
+	}
 
 	/*
 	 * A signal could leave PageWaiters set. Clearing it here if
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 22320ea27489..8469f34e6731 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -67,6 +67,7 @@
 #include <linux/ftrace.h>
 #include <linux/lockdep.h>
 #include <linux/nmi.h>
+#include <linux/psi.h>
 
 #include <asm/sections.h>
 #include <asm/tlbflush.h>
@@ -3552,15 +3553,20 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
 		enum compact_priority prio, enum compact_result *compact_result)
 {
 	struct page *page;
+	unsigned long pflags;
 	unsigned int noreclaim_flag;
 
 	if (!order)
 		return NULL;
 
+	psi_memstall_enter(&pflags);
 	noreclaim_flag = memalloc_noreclaim_save();
+
 	*compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac,
 									prio);
+
 	memalloc_noreclaim_restore(noreclaim_flag);
+	psi_memstall_leave(&pflags);
 
 	if (*compact_result <= COMPACT_INACTIVE)
 		return NULL;
@@ -3749,11 +3755,14 @@ __perform_reclaim(gfp_t gfp_mask, unsigned int order,
 	struct reclaim_state reclaim_state;
 	int progress;
 	unsigned int noreclaim_flag;
+	unsigned long pflags;
 
 	cond_resched();
 
 	/* We now go into synchronous reclaim */
 	cpuset_memory_pressure_bump();
+
+	psi_memstall_enter(&pflags);
 	noreclaim_flag = memalloc_noreclaim_save();
 	fs_reclaim_acquire(gfp_mask);
 	reclaim_state.reclaimed_slab = 0;
@@ -3765,6 +3774,7 @@ __perform_reclaim(gfp_t gfp_mask, unsigned int order,
 	current->reclaim_state = NULL;
 	fs_reclaim_release(gfp_mask);
 	memalloc_noreclaim_restore(noreclaim_flag);
+	psi_memstall_leave(&pflags);
 
 	cond_resched();
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 8d1ad48ffbcd..ee91e8cbeb5a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -49,6 +49,7 @@
 #include <linux/prefetch.h>
 #include <linux/printk.h>
 #include <linux/dax.h>
+#include <linux/psi.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -3115,6 +3116,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
 {
 	struct zonelist *zonelist;
 	unsigned long nr_reclaimed;
+	unsigned long pflags;
 	int nid;
 	unsigned int noreclaim_flag;
 	struct scan_control sc = {
@@ -3143,9 +3145,13 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
 					    sc.gfp_mask,
 					    sc.reclaim_idx);
 
+	psi_memstall_enter(&pflags);
 	noreclaim_flag = memalloc_noreclaim_save();
+
 	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
+
 	memalloc_noreclaim_restore(noreclaim_flag);
+	psi_memstall_leave(&pflags);
 
 	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
 
@@ -3565,6 +3571,7 @@ static int kswapd(void *p)
 	pgdat->kswapd_order = 0;
 	pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
 	for ( ; ; ) {
+		unsigned long pflags;
 		bool ret;
 
 		alloc_order = reclaim_order = pgdat->kswapd_order;
@@ -3601,9 +3608,15 @@ static int kswapd(void *p)
 		 */
 		trace_mm_vmscan_kswapd_wake(pgdat->node_id, classzone_idx,
 						alloc_order);
+
+		psi_memstall_enter(&pflags);
 		fs_reclaim_acquire(GFP_KERNEL);
+
 		reclaim_order = balance_pgdat(pgdat, alloc_order, classzone_idx);
+
 		fs_reclaim_release(GFP_KERNEL);
+		psi_memstall_leave(&pflags);
+
 		if (reclaim_order < alloc_order)
 			goto kswapd_try_sleep;
 	}
-- 
2.18.0

Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

[Peter Zijlstra]

On Wed, Aug 01, 2018 at 11:19:57AM -0400, Johannes Weiner wrote:
> +static bool test_state(unsigned int *tasks, int cpu, enum psi_states state)
> +{
> +	switch (state) {
> +	case PSI_IO_SOME:
> +		return tasks[NR_IOWAIT];
> +	case PSI_IO_FULL:
> +		return tasks[NR_IOWAIT] && !tasks[NR_RUNNING];
> +	case PSI_MEM_SOME:
> +		return tasks[NR_MEMSTALL];
> +	case PSI_MEM_FULL:
> +		/*
> +		 * Since we care about lost potential, things are
> +		 * fully blocked on memory when there are no other
> +		 * working tasks, but also when the CPU is actively
> +		 * being used by a reclaimer and nothing productive
> +		 * could run even if it were runnable.
> +		 */
> +		return tasks[NR_MEMSTALL] &&
> +			(!tasks[NR_RUNNING] ||
> +			 cpu_curr(cpu)->flags & PF_MEMSTALL);

I don't think you can do this, there is nothing that guarantees
cpu_curr() still exists.

> +	case PSI_CPU_SOME:
> +		return tasks[NR_RUNNING] > 1;
> +	case PSI_NONIDLE:
> +		return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] ||
> +			tasks[NR_RUNNING];
> +	default:
> +		return false;
> +	}
> +}
> +
> +static bool psi_update_stats(struct psi_group *group)
> +{
> +	u64 deltas[NR_PSI_STATES - 1] = { 0, };
> +	unsigned long missed_periods = 0;
> +	unsigned long nonidle_total = 0;
> +	u64 now, expires, period;
> +	int cpu;
> +	int s;
> +
> +	mutex_lock(&group->stat_lock);
> +
> +	/*
> +	 * Collect the per-cpu time buckets and average them into a
> +	 * single time sample that is normalized to wallclock time.
> +	 *
> +	 * For averaging, each CPU is weighted by its non-idle time in
> +	 * the sampling period. This eliminates artifacts from uneven
> +	 * loading, or even entirely idle CPUs.
> +	 *
> +	 * We don't need to synchronize against CPU hotplugging. If we
> +	 * see a CPU that's online and has samples, we incorporate it.
> +	 */
> +	for_each_online_cpu(cpu) {
> +		struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu);
> +		u32 uninitialized_var(nonidle);

urgh.. I can see why the compiler got confused. Dodgy :-)

> +
> +		BUILD_BUG_ON(PSI_NONIDLE != NR_PSI_STATES - 1);
> +
> +		for (s = PSI_NONIDLE; s >= 0; s--) {
> +			u32 time, delta;
> +
> +			time = READ_ONCE(groupc->times[s]);
> +			/*
> +			 * In addition to already concluded states, we
> +			 * also incorporate currently active states on
> +			 * the CPU, since states may last for many
> +			 * sampling periods.
> +			 *
> +			 * This way we keep our delta sampling buckets
> +			 * small (u32) and our reported pressure close
> +			 * to what's actually happening.
> +			 */
> +			if (test_state(groupc->tasks, cpu, s)) {
> +				/*
> +				 * We can race with a state change and
> +				 * need to make sure the state_start
> +				 * update is ordered against the
> +				 * updates to the live state and the
> +				 * time buckets (groupc->times).
> +				 *
> +				 * 1. If we observe task state that
> +				 * needs to be recorded, make sure we
> +				 * see state_start from when that
> +				 * state went into effect or we'll
> +				 * count time from the previous state.
> +				 *
> +				 * 2. If the time delta has already
> +				 * been added to the bucket, make sure
> +				 * we don't see it in state_start or
> +				 * we'll count it twice.
> +				 *
> +				 * If the time delta is out of
> +				 * state_start but not in the time
> +				 * bucket yet, we'll miss it entirely
> +				 * and handle it in the next period.
> +				 */
> +				smp_rmb();
> +				time += cpu_clock(cpu) - groupc->state_start;
> +			}

The alternative is adding an update to scheduler_tick(), that would
ensure you're never more than nr_cpu_ids * TICK_NSEC behind.

> +			delta = time - groupc->times_prev[s];
> +			groupc->times_prev[s] = time;
> +
> +			if (s == PSI_NONIDLE) {
> +				nonidle = nsecs_to_jiffies(delta);
> +				nonidle_total += nonidle;
> +			} else {
> +				deltas[s] += (u64)delta * nonidle;
> +			}
> +		}
> +	}

Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

[Johannes Weiner]

On Fri, Aug 03, 2018 at 06:56:41PM +0200, Peter Zijlstra wrote:
> On Wed, Aug 01, 2018 at 11:19:57AM -0400, Johannes Weiner wrote:
> > +static bool test_state(unsigned int *tasks, int cpu, enum psi_states state)
> > +{
> > +	switch (state) {
> > +	case PSI_IO_SOME:
> > +		return tasks[NR_IOWAIT];
> > +	case PSI_IO_FULL:
> > +		return tasks[NR_IOWAIT] && !tasks[NR_RUNNING];
> > +	case PSI_MEM_SOME:
> > +		return tasks[NR_MEMSTALL];
> > +	case PSI_MEM_FULL:
> > +		/*
> > +		 * Since we care about lost potential, things are
> > +		 * fully blocked on memory when there are no other
> > +		 * working tasks, but also when the CPU is actively
> > +		 * being used by a reclaimer and nothing productive
> > +		 * could run even if it were runnable.
> > +		 */
> > +		return tasks[NR_MEMSTALL] &&
> > +			(!tasks[NR_RUNNING] ||
> > +			 cpu_curr(cpu)->flags & PF_MEMSTALL);
> 
> I don't think you can do this, there is nothing that guarantees
> cpu_curr() still exists.

Argh, that's right. This needs an explicit count if we want to access
it locklessly. And you already said you didn't like that this is the
only state not derived purely from the task counters, so maybe this is
the way to go after all.

How about something like this (untested)?

diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
index b6ff46362eb3..afc39fbbf9dd 100644
--- a/include/linux/psi_types.h
+++ b/include/linux/psi_types.h
@@ -10,6 +10,7 @@ enum psi_task_count {
 	NR_IOWAIT,
 	NR_MEMSTALL,
 	NR_RUNNING,
+	NR_RECLAIMING,
 	NR_PSI_TASK_COUNTS,
 };
 
@@ -17,6 +18,7 @@ enum psi_task_count {
 #define TSK_IOWAIT	(1 << NR_IOWAIT)
 #define TSK_MEMSTALL	(1 << NR_MEMSTALL)
 #define TSK_RUNNING	(1 << NR_RUNNING)
+#define TSK_RECLAIMING	(1 << NR_RECLAIMING)
 
 /* Resources that workloads could be stalled on */
 enum psi_res {
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e53137df405b..90fd813dd7c2 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3517,6 +3517,7 @@ static void __sched notrace __schedule(bool preempt)
 		 */
 		++*switch_count;
 
+		psi_switch(rq, prev, next);
 		trace_sched_switch(preempt, prev, next);
 
 		/* Also unlocks the rq: */
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index a20f885da66f..352c3a032ff0 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -209,8 +209,7 @@ static bool test_state(unsigned int *tasks, int cpu, enum psi_states state)
 		 * could run even if it were runnable.
 		 */
 		return tasks[NR_MEMSTALL] &&
-			(!tasks[NR_RUNNING] ||
-			 cpu_curr(cpu)->flags & PF_MEMSTALL);
+			(!tasks[NR_RUNNING] || tasks[NR_RECLAIMING]);
 	case PSI_CPU_SOME:
 		return tasks[NR_RUNNING] > 1;
 	case PSI_NONIDLE:
@@ -530,7 +529,7 @@ void psi_memstall_enter(unsigned long *flags)
 	update_rq_clock(rq);
 
 	current->flags |= PF_MEMSTALL;
-	psi_task_change(current, rq_clock(rq), 0, TSK_MEMSTALL);
+	psi_task_change(current, rq_clock(rq), 0, TSK_MEMSTALL|TSK_RECLAIMING);
 
 	rq_unlock_irq(rq, &rf);
 }
@@ -561,7 +560,7 @@ void psi_memstall_leave(unsigned long *flags)
 	update_rq_clock(rq);
 
 	current->flags &= ~PF_MEMSTALL;
-	psi_task_change(current, rq_clock(rq), TSK_MEMSTALL, 0);
+	psi_task_change(current, rq_clock(rq), TSK_MEMSTALL|TSK_RECLAIMING, 0);
 
 	rq_unlock_irq(rq, &rf);
 }
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index f3e0267eb47d..2babdd53715d 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -127,12 +127,26 @@ static inline void psi_ttwu_dequeue(struct task_struct *p)
 		__task_rq_unlock(rq, &rf);
 	}
 }
+
+static inline void psi_switch(struct rq *rq, struct task_struct *prev,
+			      struct task_struct *next)
+{
+	if (psi_disabled)
+		return;
+
+	if (unlikely(prev->flags & PF_MEMSTALL))
+		psi_task_change(prev, rq_clock(rq), TSK_RECLAIMING, 0);
+	if (unlikely(next->flags & PF_MEMSTALL))
+		psi_task_change(next, rq_clock(rq), 0, TSK_RECLAIMING);
+}
 #else /* CONFIG_PSI */
 static inline void psi_enqueue(struct rq *rq, struct task_struct *p,
 			       bool wakeup) {}
 static inline void psi_dequeue(struct rq *rq, struct task_struct *p,
 			       bool sleep) {}
 static inline void psi_ttwu_dequeue(struct task_struct *p) {}
+static inline void psi_switch(struct rq *rq, struct task_struct *prev,
+			      struct task_struct *next) {}
 #endif /* CONFIG_PSI */
 
 #ifdef CONFIG_SCHED_INFO

Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

[Peter Zijlstra]

On Mon, Aug 06, 2018 at 11:05:50AM -0400, Johannes Weiner wrote:
> Argh, that's right. This needs an explicit count if we want to access
> it locklessly. And you already said you didn't like that this is the
> only state not derived purely from the task counters, so maybe this is
> the way to go after all.
> 
> How about something like this (untested)?


> +static inline void psi_switch(struct rq *rq, struct task_struct *prev,
> +			      struct task_struct *next)
> +{
> +	if (psi_disabled)
> +		return;
> +
> +	if (unlikely(prev->flags & PF_MEMSTALL))
> +		psi_task_change(prev, rq_clock(rq), TSK_RECLAIMING, 0);
> +	if (unlikely(next->flags & PF_MEMSTALL))
> +		psi_task_change(next, rq_clock(rq), 0, TSK_RECLAIMING);
> +}


Urgh... can't say I really like that.

I would really rather do that scheduler_tick() thing to avoid the remote
update. The tick is a lot less hot than the switch path and esp.
next->flags might be a cold line (prev->flags is typically the same line
as prev->state so we already have that, but I don't think anybody now
looks at next->flags or its line, so that'd be cold load).

Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

[Johannes Weiner]

On Mon, Aug 06, 2018 at 05:25:28PM +0200, Peter Zijlstra wrote:
> On Mon, Aug 06, 2018 at 11:05:50AM -0400, Johannes Weiner wrote:
> > Argh, that's right. This needs an explicit count if we want to access
> > it locklessly. And you already said you didn't like that this is the
> > only state not derived purely from the task counters, so maybe this is
> > the way to go after all.
> > 
> > How about something like this (untested)?
> 
> 
> > +static inline void psi_switch(struct rq *rq, struct task_struct *prev,
> > +			      struct task_struct *next)
> > +{
> > +	if (psi_disabled)
> > +		return;
> > +
> > +	if (unlikely(prev->flags & PF_MEMSTALL))
> > +		psi_task_change(prev, rq_clock(rq), TSK_RECLAIMING, 0);
> > +	if (unlikely(next->flags & PF_MEMSTALL))
> > +		psi_task_change(next, rq_clock(rq), 0, TSK_RECLAIMING);
> > +}
> 
> 
> Urgh... can't say I really like that.
> 
> I would really rather do that scheduler_tick() thing to avoid the remote
> update. The tick is a lot less hot than the switch path and esp.
> next->flags might be a cold line (prev->flags is typically the same line
> as prev->state so we already have that, but I don't think anybody now
> looks at next->flags or its line, so that'd be cold load).

Okay, the tick updater sounds like a much better option then. HZ
frequency should produce more than recent enough data.

That means we will retain the not-so-nice PF_MEMSTALL flag test under
rq lock, but it'll eliminate most of that memory ordering headache.

I'll do that. Thanks!

Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

[Johannes Weiner]

On Fri, Aug 03, 2018 at 06:56:41PM +0200, Peter Zijlstra wrote:
> On Wed, Aug 01, 2018 at 11:19:57AM -0400, Johannes Weiner wrote:
> > +static bool psi_update_stats(struct psi_group *group)
> > +{
> > +	u64 deltas[NR_PSI_STATES - 1] = { 0, };
> > +	unsigned long missed_periods = 0;
> > +	unsigned long nonidle_total = 0;
> > +	u64 now, expires, period;
> > +	int cpu;
> > +	int s;
> > +
> > +	mutex_lock(&group->stat_lock);
> > +
> > +	/*
> > +	 * Collect the per-cpu time buckets and average them into a
> > +	 * single time sample that is normalized to wallclock time.
> > +	 *
> > +	 * For averaging, each CPU is weighted by its non-idle time in
> > +	 * the sampling period. This eliminates artifacts from uneven
> > +	 * loading, or even entirely idle CPUs.
> > +	 *
> > +	 * We don't need to synchronize against CPU hotplugging. If we
> > +	 * see a CPU that's online and has samples, we incorporate it.
> > +	 */
> > +	for_each_online_cpu(cpu) {
> > +		struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu);
> > +		u32 uninitialized_var(nonidle);
> 
> urgh.. I can see why the compiler got confused. Dodgy :-)

:-) I think we can make this cleaner. Something like this (modulo the
READ_ONCE/WRITE_ONCE you pointed out in the other email)?

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index abccfddba5d5..ce6f02ada1cd 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -220,6 +220,49 @@ static bool test_state(unsigned int *tasks, enum psi_states state)
 	}
 }
 
+static u32 read_update_delta(struct psi_group_cpu *groupc,
+			     enum psi_states state, int cpu)
+{
+	u32 time, delta;
+
+	time = READ_ONCE(groupc->times[state]);
+	/*
+	 * In addition to already concluded states, we also
+	 * incorporate currently active states on the CPU, since
+	 * states may last for many sampling periods.
+	 *
+	 * This way we keep our delta sampling buckets small (u32) and
+	 * our reported pressure close to what's actually happening.
+	 */
+	if (test_state(groupc->tasks, state)) {
+		/*
+		 * We can race with a state change and need to make
+		 * sure the state_start update is ordered against the
+		 * updates to the live state and the time buckets
+		 * (groupc->times).
+		 *
+		 * 1. If we observe task state that needs to be
+		 * recorded, make sure we see state_start from when
+		 * that state went into effect or we'll count time
+		 * from the previous state.
+		 *
+		 * 2. If the time delta has already been added to the
+		 * bucket, make sure we don't see it in state_start or
+		 * we'll count it twice.
+		 *
+		 * If the time delta is out of state_start but not in
+		 * the time bucket yet, we'll miss it entirely and
+		 * handle it in the next period.
+		 */
+		smp_rmb();
+		time += cpu_clock(cpu) - groupc->state_start;
+	}
+	delta = time - groupc->times_prev[state];
+	groupc->times_prev[state] = time;
+
+	return delta;
+}
+
 static bool psi_update_stats(struct psi_group *group)
 {
 	u64 deltas[NR_PSI_STATES - 1] = { 0, };
@@ -244,60 +287,17 @@ static bool psi_update_stats(struct psi_group *group)
 	 */
 	for_each_online_cpu(cpu) {
 		struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu);
-		u32 uninitialized_var(nonidle);
-
-		BUILD_BUG_ON(PSI_NONIDLE != NR_PSI_STATES - 1);
-
-		for (s = PSI_NONIDLE; s >= 0; s--) {
-			u32 time, delta;
-
-			time = READ_ONCE(groupc->times[s]);
-			/*
-			 * In addition to already concluded states, we
-			 * also incorporate currently active states on
-			 * the CPU, since states may last for many
-			 * sampling periods.
-			 *
-			 * This way we keep our delta sampling buckets
-			 * small (u32) and our reported pressure close
-			 * to what's actually happening.
-			 */
-			if (test_state(groupc->tasks, cpu, s)) {
-				/*
-				 * We can race with a state change and
-				 * need to make sure the state_start
-				 * update is ordered against the
-				 * updates to the live state and the
-				 * time buckets (groupc->times).
-				 *
-				 * 1. If we observe task state that
-				 * needs to be recorded, make sure we
-				 * see state_start from when that
-				 * state went into effect or we'll
-				 * count time from the previous state.
-				 *
-				 * 2. If the time delta has already
-				 * been added to the bucket, make sure
-				 * we don't see it in state_start or
-				 * we'll count it twice.
-				 *
-				 * If the time delta is out of
-				 * state_start but not in the time
-				 * bucket yet, we'll miss it entirely
-				 * and handle it in the next period.
-				 */
-				smp_rmb();
-				time += cpu_clock(cpu) - groupc->state_start;
-			}
-			delta = time - groupc->times_prev[s];
-			groupc->times_prev[s] = time;
-
-			if (s == PSI_NONIDLE) {
-				nonidle = nsecs_to_jiffies(delta);
-				nonidle_total += nonidle;
-			} else {
-				deltas[s] += (u64)delta * nonidle;
-			}
+		u32 nonidle;
+
+		nonidle = read_update_delta(groupc, PSI_NONIDLE, cpu);
+		nonidle = nsecs_to_jiffies(nonidle);
+		nonidle_total += nonidle;
+
+		for (s = 0; s < PSI_NONIDLE; s++) {
+			u32 delta;
+
+			delta = read_update_delta(groupc, s, cpu);
+			deltas[s] += (u64)delta * nonidle;
 		}
 	}
 

Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

[Peter Zijlstra]

On Mon, Aug 06, 2018 at 11:19:28AM -0400, Johannes Weiner wrote:
> On Fri, Aug 03, 2018 at 06:56:41PM +0200, Peter Zijlstra wrote:
> > On Wed, Aug 01, 2018 at 11:19:57AM -0400, Johannes Weiner wrote:

> > > +		u32 uninitialized_var(nonidle);
> > 
> > urgh.. I can see why the compiler got confused. Dodgy :-)
> 
> :-) I think we can make this cleaner. Something like this (modulo the
> READ_ONCE/WRITE_ONCE you pointed out in the other email)?
> 

> @@ -244,60 +287,17 @@ static bool psi_update_stats(struct psi_group *group)
>  	 */
>  	for_each_online_cpu(cpu) {
>  		struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu);
> +		u32 nonidle;
> +
> +		nonidle = read_update_delta(groupc, PSI_NONIDLE, cpu);
> +		nonidle = nsecs_to_jiffies(nonidle);
> +		nonidle_total += nonidle;
> +
> +		for (s = 0; s < PSI_NONIDLE; s++) {
> +			u32 delta;
> +
> +			delta = read_update_delta(groupc, s, cpu);
> +			deltas[s] += (u64)delta * nonidle;
>  		}
>  	}

Yes, much clearer, thanks!

Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

[Johannes Weiner]

Hi,

a quick update on that feedback before I send out v4:

On Fri, Aug 03, 2018 at 06:56:41PM +0200, Peter Zijlstra wrote:
> On Wed, Aug 01, 2018 at 11:19:57AM -0400, Johannes Weiner wrote:
> > +static bool test_state(unsigned int *tasks, int cpu, enum psi_states state)
> > +{
> > +	switch (state) {
> > +	case PSI_IO_SOME:
> > +		return tasks[NR_IOWAIT];
> > +	case PSI_IO_FULL:
> > +		return tasks[NR_IOWAIT] && !tasks[NR_RUNNING];
> > +	case PSI_MEM_SOME:
> > +		return tasks[NR_MEMSTALL];
> > +	case PSI_MEM_FULL:
> > +		/*
> > +		 * Since we care about lost potential, things are
> > +		 * fully blocked on memory when there are no other
> > +		 * working tasks, but also when the CPU is actively
> > +		 * being used by a reclaimer and nothing productive
> > +		 * could run even if it were runnable.
> > +		 */
> > +		return tasks[NR_MEMSTALL] &&
> > +			(!tasks[NR_RUNNING] ||
> > +			 cpu_curr(cpu)->flags & PF_MEMSTALL);
> 
> I don't think you can do this, there is nothing that guarantees
> cpu_curr() still exists.

As discussed later in this thread, I've replaced this with time
sampling from inside scheduler_tick(): in the unlikely event that
rq->curr is PF_MEMSTALL, it'll record TICK_NSEC worth of MEM_FULL.

However:

> > +		for (s = PSI_NONIDLE; s >= 0; s--) {
> > +			u32 time, delta;
> > +
> > +			time = READ_ONCE(groupc->times[s]);
> > +			/*
> > +			 * In addition to already concluded states, we
> > +			 * also incorporate currently active states on
> > +			 * the CPU, since states may last for many
> > +			 * sampling periods.
> > +			 *
> > +			 * This way we keep our delta sampling buckets
> > +			 * small (u32) and our reported pressure close
> > +			 * to what's actually happening.
> > +			 */
> > +			if (test_state(groupc->tasks, cpu, s)) {
> > +				/*
> > +				 * We can race with a state change and
> > +				 * need to make sure the state_start
> > +				 * update is ordered against the
> > +				 * updates to the live state and the
> > +				 * time buckets (groupc->times).
> > +				 *
> > +				 * 1. If we observe task state that
> > +				 * needs to be recorded, make sure we
> > +				 * see state_start from when that
> > +				 * state went into effect or we'll
> > +				 * count time from the previous state.
> > +				 *
> > +				 * 2. If the time delta has already
> > +				 * been added to the bucket, make sure
> > +				 * we don't see it in state_start or
> > +				 * we'll count it twice.
> > +				 *
> > +				 * If the time delta is out of
> > +				 * state_start but not in the time
> > +				 * bucket yet, we'll miss it entirely
> > +				 * and handle it in the next period.
> > +				 */
> > +				smp_rmb();
> > +				time += cpu_clock(cpu) - groupc->state_start;
> > +			}
> 
> The alternative is adding an update to scheduler_tick(), that would
> ensure you're never more than nr_cpu_ids * TICK_NSEC behind.

I wasn't able to convert *all* states to tick updates like this.

The reason is that, while testing rq->curr for PF_MEMSTALL is cheap,
other tasks associated with the rq could be from any cgroup in the
system. That means we'd have to do for_each_cgroup() on every tick to
keep the groupc->times that closely uptodate, and that wouldn't scale.
We tend to have hundreds of them, some setups have thousands.

Since we don't need to be *that* current, I left the on-demand update
inside the aggregator for now. It's a bit trickier, but much cheaper.

Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

[Peter Zijlstra]

On Tue, Aug 21, 2018 at 03:44:13PM -0400, Johannes Weiner wrote:

> > > +		for (s = PSI_NONIDLE; s >= 0; s--) {
> > > +			u32 time, delta;
> > > +
> > > +			time = READ_ONCE(groupc->times[s]);
> > > +			/*
> > > +			 * In addition to already concluded states, we
> > > +			 * also incorporate currently active states on
> > > +			 * the CPU, since states may last for many
> > > +			 * sampling periods.
> > > +			 *
> > > +			 * This way we keep our delta sampling buckets
> > > +			 * small (u32) and our reported pressure close
> > > +			 * to what's actually happening.
> > > +			 */
> > > +			if (test_state(groupc->tasks, cpu, s)) {
> > > +				/*
> > > +				 * We can race with a state change and
> > > +				 * need to make sure the state_start
> > > +				 * update is ordered against the
> > > +				 * updates to the live state and the
> > > +				 * time buckets (groupc->times).
> > > +				 *
> > > +				 * 1. If we observe task state that
> > > +				 * needs to be recorded, make sure we
> > > +				 * see state_start from when that
> > > +				 * state went into effect or we'll
> > > +				 * count time from the previous state.
> > > +				 *
> > > +				 * 2. If the time delta has already
> > > +				 * been added to the bucket, make sure
> > > +				 * we don't see it in state_start or
> > > +				 * we'll count it twice.
> > > +				 *
> > > +				 * If the time delta is out of
> > > +				 * state_start but not in the time
> > > +				 * bucket yet, we'll miss it entirely
> > > +				 * and handle it in the next period.
> > > +				 */
> > > +				smp_rmb();
> > > +				time += cpu_clock(cpu) - groupc->state_start;
> > > +			}
> > 
> > The alternative is adding an update to scheduler_tick(), that would
> > ensure you're never more than nr_cpu_ids * TICK_NSEC behind.
> 
> I wasn't able to convert *all* states to tick updates like this.
> 
> The reason is that, while testing rq->curr for PF_MEMSTALL is cheap,
> other tasks associated with the rq could be from any cgroup in the
> system. That means we'd have to do for_each_cgroup() on every tick to
> keep the groupc->times that closely uptodate, and that wouldn't scale.
> We tend to have hundreds of them, some setups have thousands.
> 
> Since we don't need to be *that* current, I left the on-demand update
> inside the aggregator for now. It's a bit trickier, but much cheaper.

ARGH indeed; I was thinking we only need to update current. But because
we're tracking blocked state that doesn't work.

Sorry for that :/

Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

[Peter Zijlstra]

On Wed, Aug 01, 2018 at 11:19:57AM -0400, Johannes Weiner wrote:
> +static bool psi_update_stats(struct psi_group *group)
> +{
> +	u64 deltas[NR_PSI_STATES - 1] = { 0, };
> +	unsigned long missed_periods = 0;
> +	unsigned long nonidle_total = 0;
> +	u64 now, expires, period;
> +	int cpu;
> +	int s;
> +
> +	mutex_lock(&group->stat_lock);
> +
> +	/*
> +	 * Collect the per-cpu time buckets and average them into a
> +	 * single time sample that is normalized to wallclock time.
> +	 *
> +	 * For averaging, each CPU is weighted by its non-idle time in
> +	 * the sampling period. This eliminates artifacts from uneven
> +	 * loading, or even entirely idle CPUs.
> +	 *
> +	 * We don't need to synchronize against CPU hotplugging. If we
> +	 * see a CPU that's online and has samples, we incorporate it.
> +	 */
> +	for_each_online_cpu(cpu) {

I'm still puzzled by this.. for 99% of the machines online == possible.
Why not always iterate possible and leave it at that? This is hardly a
fast path.

Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

[Johannes Weiner]

On Fri, Aug 03, 2018 at 07:07:33PM +0200, Peter Zijlstra wrote:
> On Wed, Aug 01, 2018 at 11:19:57AM -0400, Johannes Weiner wrote:
> > +static bool psi_update_stats(struct psi_group *group)
> > +{
> > +	u64 deltas[NR_PSI_STATES - 1] = { 0, };
> > +	unsigned long missed_periods = 0;
> > +	unsigned long nonidle_total = 0;
> > +	u64 now, expires, period;
> > +	int cpu;
> > +	int s;
> > +
> > +	mutex_lock(&group->stat_lock);
> > +
> > +	/*
> > +	 * Collect the per-cpu time buckets and average them into a
> > +	 * single time sample that is normalized to wallclock time.
> > +	 *
> > +	 * For averaging, each CPU is weighted by its non-idle time in
> > +	 * the sampling period. This eliminates artifacts from uneven
> > +	 * loading, or even entirely idle CPUs.
> > +	 *
> > +	 * We don't need to synchronize against CPU hotplugging. If we
> > +	 * see a CPU that's online and has samples, we incorporate it.
> > +	 */
> > +	for_each_online_cpu(cpu) {
> 
> I'm still puzzled by this.. for 99% of the machines online == possible.
> Why not always iterate possible and leave it at that? This is hardly a
> fast path.

Hmm, you're right, that makes things much simpler. I guess I'm mostly
worried about the 1% where this significantly differs, but it looks
like we're smarter than simply doing CONFIG_NR_CPUS for the possible
map, and we can easily stomach a bit of discrepancy in this path.

I'll change that to possible and delete/update the third paragraph.

Thanks

Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

[Peter Zijlstra]

On Wed, Aug 01, 2018 at 11:19:57AM -0400, Johannes Weiner wrote:
> +	/* total= */
> +	for (s = 0; s < NR_PSI_STATES - 1; s++)
> +		group->total[s] += div_u64(deltas[s], max(nonidle_total, 1UL));

Just a nit; probably not worth fixing.

This looses the remainder of that division. But since the divisor is
variable it becomes really hard to not loose something at some point.

Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

[Peter Zijlstra]

On Wed, Aug 01, 2018 at 11:19:57AM -0400, Johannes Weiner wrote:
> +			time = READ_ONCE(groupc->times[s]);
> +			/*
> +			 * In addition to already concluded states, we
> +			 * also incorporate currently active states on
> +			 * the CPU, since states may last for many
> +			 * sampling periods.
> +			 *
> +			 * This way we keep our delta sampling buckets
> +			 * small (u32) and our reported pressure close
> +			 * to what's actually happening.
> +			 */
> +			if (test_state(groupc->tasks, cpu, s)) {
> +				/*
> +				 * We can race with a state change and
> +				 * need to make sure the state_start
> +				 * update is ordered against the
> +				 * updates to the live state and the
> +				 * time buckets (groupc->times).
> +				 *
> +				 * 1. If we observe task state that
> +				 * needs to be recorded, make sure we
> +				 * see state_start from when that
> +				 * state went into effect or we'll
> +				 * count time from the previous state.
> +				 *
> +				 * 2. If the time delta has already
> +				 * been added to the bucket, make sure
> +				 * we don't see it in state_start or
> +				 * we'll count it twice.
> +				 *
> +				 * If the time delta is out of
> +				 * state_start but not in the time
> +				 * bucket yet, we'll miss it entirely
> +				 * and handle it in the next period.
> +				 */
> +				smp_rmb();
> +				time += cpu_clock(cpu) - groupc->state_start;
> +			}

As is, groupc->state_start needs a READ_ONCE() above and a WRITE_ONCE()
below. But like stated earlier, doing an update in scheduler_tick() is
probably easier.

> +static void psi_group_change(struct psi_group *group, int cpu, u64 now,
> +			     unsigned int clear, unsigned int set)
> +{
> +	struct psi_group_cpu *groupc;
> +	unsigned int t, m;
> +	u32 delta;
> +
> +	groupc = per_cpu_ptr(group->pcpu, cpu);
> +
> +	/*
> +	 * First we assess the aggregate resource states these CPU's
> +	 * tasks have been in since the last change, and account any
> +	 * SOME and FULL time that may have resulted in.
> +	 *
> +	 * Then we update the task counts according to the state
> +	 * change requested through the @clear and @set bits.
> +	 */
> +
> +	delta = now - groupc->state_start;
> +	groupc->state_start = now;
> +
> +	/*
> +	 * Update state_start before recording time in the sampling
> +	 * buckets and changing task counts, to prevent a racing
> +	 * aggregation from counting the delta twice or attributing it
> +	 * to an old state.
> +	 */
> +	smp_wmb();
> +
> +	if (test_state(groupc->tasks, cpu, PSI_IO_SOME)) {
> +		groupc->times[PSI_IO_SOME] += delta;
> +		if (test_state(groupc->tasks, cpu, PSI_IO_FULL))
> +			groupc->times[PSI_IO_FULL] += delta;
> +	}
> +	if (test_state(groupc->tasks, cpu, PSI_MEM_SOME)) {
> +		groupc->times[PSI_MEM_SOME] += delta;
> +		if (test_state(groupc->tasks, cpu, PSI_MEM_FULL))
> +			groupc->times[PSI_MEM_FULL] += delta;
> +	}

Might we worth checking the compiler does the right thing here and
optimizes this branch fest into something sensible.

> +	if (test_state(groupc->tasks, cpu, PSI_CPU_SOME))
> +		groupc->times[PSI_CPU_SOME] += delta;
> +	if (test_state(groupc->tasks, cpu, PSI_NONIDLE))
> +		groupc->times[PSI_NONIDLE] += delta;

Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

[Johannes Weiner]

On Fri, Aug 03, 2018 at 07:21:39PM +0200, Peter Zijlstra wrote:
> On Wed, Aug 01, 2018 at 11:19:57AM -0400, Johannes Weiner wrote:
> > +			time = READ_ONCE(groupc->times[s]);
> > +			/*
> > +			 * In addition to already concluded states, we
> > +			 * also incorporate currently active states on
> > +			 * the CPU, since states may last for many
> > +			 * sampling periods.
> > +			 *
> > +			 * This way we keep our delta sampling buckets
> > +			 * small (u32) and our reported pressure close
> > +			 * to what's actually happening.
> > +			 */
> > +			if (test_state(groupc->tasks, cpu, s)) {
> > +				/*
> > +				 * We can race with a state change and
> > +				 * need to make sure the state_start
> > +				 * update is ordered against the
> > +				 * updates to the live state and the
> > +				 * time buckets (groupc->times).
> > +				 *
> > +				 * 1. If we observe task state that
> > +				 * needs to be recorded, make sure we
> > +				 * see state_start from when that
> > +				 * state went into effect or we'll
> > +				 * count time from the previous state.
> > +				 *
> > +				 * 2. If the time delta has already
> > +				 * been added to the bucket, make sure
> > +				 * we don't see it in state_start or
> > +				 * we'll count it twice.
> > +				 *
> > +				 * If the time delta is out of
> > +				 * state_start but not in the time
> > +				 * bucket yet, we'll miss it entirely
> > +				 * and handle it in the next period.
> > +				 */
> > +				smp_rmb();
> > +				time += cpu_clock(cpu) - groupc->state_start;
> > +			}
> 
> As is, groupc->state_start needs a READ_ONCE() above and a WRITE_ONCE()
> below. But like stated earlier, doing an update in scheduler_tick() is
> probably easier.

I've wrapped these in READ_ONCE/WRITE_ONCE.

> > +static void psi_group_change(struct psi_group *group, int cpu, u64 now,
> > +			     unsigned int clear, unsigned int set)
> > +{
> > +	struct psi_group_cpu *groupc;
> > +	unsigned int t, m;
> > +	u32 delta;
> > +
> > +	groupc = per_cpu_ptr(group->pcpu, cpu);
> > +
> > +	/*
> > +	 * First we assess the aggregate resource states these CPU's
> > +	 * tasks have been in since the last change, and account any
> > +	 * SOME and FULL time that may have resulted in.
> > +	 *
> > +	 * Then we update the task counts according to the state
> > +	 * change requested through the @clear and @set bits.
> > +	 */
> > +
> > +	delta = now - groupc->state_start;
> > +	groupc->state_start = now;
> > +
> > +	/*
> > +	 * Update state_start before recording time in the sampling
> > +	 * buckets and changing task counts, to prevent a racing
> > +	 * aggregation from counting the delta twice or attributing it
> > +	 * to an old state.
> > +	 */
> > +	smp_wmb();
> > +
> > +	if (test_state(groupc->tasks, cpu, PSI_IO_SOME)) {
> > +		groupc->times[PSI_IO_SOME] += delta;
> > +		if (test_state(groupc->tasks, cpu, PSI_IO_FULL))
> > +			groupc->times[PSI_IO_FULL] += delta;
> > +	}
> > +	if (test_state(groupc->tasks, cpu, PSI_MEM_SOME)) {
> > +		groupc->times[PSI_MEM_SOME] += delta;
> > +		if (test_state(groupc->tasks, cpu, PSI_MEM_FULL))
> > +			groupc->times[PSI_MEM_FULL] += delta;
> > +	}
> 
> Might we worth checking the compiler does the right thing here and
> optimizes this branch fest into something sensible.

Yup, the results looked good. It recognizes that SOME and FULL have
overlapping conditions and then lays out the branches such that it
does not have to do redundant tests. It also recognizes that NONIDLE
is true when any of the other states is true and collapses that.

> > +	if (test_state(groupc->tasks, cpu, PSI_CPU_SOME))
> > +		groupc->times[PSI_CPU_SOME] += delta;
> > +	if (test_state(groupc->tasks, cpu, PSI_NONIDLE))
> > +		groupc->times[PSI_NONIDLE] += delta;

Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

[Peter Zijlstra]

On Tue, Aug 21, 2018 at 04:11:15PM -0400, Johannes Weiner wrote:
> On Fri, Aug 03, 2018 at 07:21:39PM +0200, Peter Zijlstra wrote:
> > On Wed, Aug 01, 2018 at 11:19:57AM -0400, Johannes Weiner wrote:
> > > +			time = READ_ONCE(groupc->times[s]);
> > > +			/*
> > > +			 * In addition to already concluded states, we
> > > +			 * also incorporate currently active states on
> > > +			 * the CPU, since states may last for many
> > > +			 * sampling periods.
> > > +			 *
> > > +			 * This way we keep our delta sampling buckets
> > > +			 * small (u32) and our reported pressure close
> > > +			 * to what's actually happening.
> > > +			 */
> > > +			if (test_state(groupc->tasks, cpu, s)) {
> > > +				/*
> > > +				 * We can race with a state change and
> > > +				 * need to make sure the state_start
> > > +				 * update is ordered against the
> > > +				 * updates to the live state and the
> > > +				 * time buckets (groupc->times).
> > > +				 *
> > > +				 * 1. If we observe task state that
> > > +				 * needs to be recorded, make sure we
> > > +				 * see state_start from when that
> > > +				 * state went into effect or we'll
> > > +				 * count time from the previous state.
> > > +				 *
> > > +				 * 2. If the time delta has already
> > > +				 * been added to the bucket, make sure
> > > +				 * we don't see it in state_start or
> > > +				 * we'll count it twice.
> > > +				 *
> > > +				 * If the time delta is out of
> > > +				 * state_start but not in the time
> > > +				 * bucket yet, we'll miss it entirely
> > > +				 * and handle it in the next period.
> > > +				 */
> > > +				smp_rmb();
> > > +				time += cpu_clock(cpu) - groupc->state_start;
> > > +			}
> > 
> > As is, groupc->state_start needs a READ_ONCE() above and a WRITE_ONCE()
> > below. But like stated earlier, doing an update in scheduler_tick() is
> > probably easier.
> 
> I've wrapped these in READ_ONCE/WRITE_ONCE.

I just realized, these are u64, so READ_ONCE/WRITE_ONCE will not work
correct on 32bit.

Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

[Johannes Weiner]

On Wed, Aug 22, 2018 at 11:10:24AM +0200, Peter Zijlstra wrote:
> On Tue, Aug 21, 2018 at 04:11:15PM -0400, Johannes Weiner wrote:
> > On Fri, Aug 03, 2018 at 07:21:39PM +0200, Peter Zijlstra wrote:
> > > On Wed, Aug 01, 2018 at 11:19:57AM -0400, Johannes Weiner wrote:
> > > > +			time = READ_ONCE(groupc->times[s]);
> > > > +			/*
> > > > +			 * In addition to already concluded states, we
> > > > +			 * also incorporate currently active states on
> > > > +			 * the CPU, since states may last for many
> > > > +			 * sampling periods.
> > > > +			 *
> > > > +			 * This way we keep our delta sampling buckets
> > > > +			 * small (u32) and our reported pressure close
> > > > +			 * to what's actually happening.
> > > > +			 */
> > > > +			if (test_state(groupc->tasks, cpu, s)) {
> > > > +				/*
> > > > +				 * We can race with a state change and
> > > > +				 * need to make sure the state_start
> > > > +				 * update is ordered against the
> > > > +				 * updates to the live state and the
> > > > +				 * time buckets (groupc->times).
> > > > +				 *
> > > > +				 * 1. If we observe task state that
> > > > +				 * needs to be recorded, make sure we
> > > > +				 * see state_start from when that
> > > > +				 * state went into effect or we'll
> > > > +				 * count time from the previous state.
> > > > +				 *
> > > > +				 * 2. If the time delta has already
> > > > +				 * been added to the bucket, make sure
> > > > +				 * we don't see it in state_start or
> > > > +				 * we'll count it twice.
> > > > +				 *
> > > > +				 * If the time delta is out of
> > > > +				 * state_start but not in the time
> > > > +				 * bucket yet, we'll miss it entirely
> > > > +				 * and handle it in the next period.
> > > > +				 */
> > > > +				smp_rmb();
> > > > +				time += cpu_clock(cpu) - groupc->state_start;
> > > > +			}
> > > 
> > > As is, groupc->state_start needs a READ_ONCE() above and a WRITE_ONCE()
> > > below. But like stated earlier, doing an update in scheduler_tick() is
> > > probably easier.
> > 
> > I've wrapped these in READ_ONCE/WRITE_ONCE.
> 
> I just realized, these are u64, so READ_ONCE/WRITE_ONCE will not work
> correct on 32bit.

Ah, right.

Actually, that race described in the comment above - "If the time
delta is out of state_start but not in the time bucket yet, we'll miss
it entirely and handle it in the next period" - can cause bogus time
samples if state persists for more than 2s. Because if we observed a
live state and included it in our private copy of the time bucket
(times_prev), missing the delta in transit to the time bucket in the
next aggregation results in times_prev being ahead of 'time', which
causes the delta to underflow into a bogusly large sample.

Memory barriers alone cannot guarantee full coherency here (neither
seeing the delta twice, nor missing it entirely) so I'm switching this
over to seqcount to make sure the aggregator sees something sensible.

And then I don't need the READ_ONCE/WRITE_ONCE.

[PATCH 9/9] psi: cgroup support

[Johannes Weiner]

On a system that executes multiple cgrouped jobs and independent
workloads, we don't just care about the health of the overall system,
but also that of individual jobs, so that we can ensure individual job
health, fairness between jobs, or prioritize some jobs over others.

This patch implements pressure stall tracking for cgroups. In kernels
with CONFIG_PSI=y, cgroup2 groups will have cpu.pressure,
memory.pressure, and io.pressure files that track aggregate pressure
stall times for only the tasks inside the cgroup.

v3:
- fix copy-paste indentation screwups

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 Documentation/accounting/psi.txt |  9 ++++
 Documentation/cgroup-v2.txt      | 18 +++++++
 include/linux/cgroup-defs.h      |  4 ++
 include/linux/cgroup.h           | 15 ++++++
 include/linux/psi.h              | 25 ++++++++++
 init/Kconfig                     |  4 ++
 kernel/cgroup/cgroup.c           | 45 +++++++++++++++++-
 kernel/sched/psi.c               | 81 +++++++++++++++++++++++++++++++-
 8 files changed, 197 insertions(+), 4 deletions(-)

diff --git a/Documentation/accounting/psi.txt b/Documentation/accounting/psi.txt
index 51e7ef14142e..e051810d5127 100644
--- a/Documentation/accounting/psi.txt
+++ b/Documentation/accounting/psi.txt
@@ -62,3 +62,12 @@ well as medium and long term trends. The total absolute stall time is
 tracked and exported as well, to allow detection of latency spikes
 which wouldn't necessarily make a dent in the time averages, or to
 average trends over custom time frames.
+
+Cgroup2 interface
+=================
+
+In a system with a CONFIG_CGROUP=y kernel and the cgroup2 filesystem
+mounted, pressure stall information is also tracked for tasks grouped
+into cgroups. Each subdirectory in the cgroupfs mountpoint contains
+cpu.pressure, memory.pressure, and io.pressure files; the format is
+the same as the /proc/pressure/ files.
diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index 74cdeaed9f7a..a22879dba019 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -963,6 +963,12 @@ All time durations are in microseconds.
 	$PERIOD duration.  "max" for $MAX indicates no limit.  If only
 	one number is written, $MAX is updated.
 
+  cpu.pressure
+	A read-only nested-key file which exists on non-root cgroups.
+
+	Shows pressure stall information for CPU. See
+	Documentation/accounting/psi.txt for details.
+
 
 Memory
 ------
@@ -1199,6 +1205,12 @@ PAGE_SIZE multiple when read back.
 	Swap usage hard limit.  If a cgroup's swap usage reaches this
 	limit, anonymous memory of the cgroup will not be swapped out.
 
+  memory.pressure
+	A read-only nested-key file which exists on non-root cgroups.
+
+	Shows pressure stall information for memory. See
+	Documentation/accounting/psi.txt for details.
+
 
 Usage Guidelines
 ~~~~~~~~~~~~~~~~
@@ -1334,6 +1346,12 @@ IO Interface Files
 
 	  8:16 rbps=2097152 wbps=max riops=max wiops=max
 
+  io.pressure
+	A read-only nested-key file which exists on non-root cgroups.
+
+	Shows pressure stall information for IO. See
+	Documentation/accounting/psi.txt for details.
+
 
 Writeback
 ~~~~~~~~~
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index dc5b70449dc6..280f18da956a 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -20,6 +20,7 @@
 #include <linux/u64_stats_sync.h>
 #include <linux/workqueue.h>
 #include <linux/bpf-cgroup.h>
+#include <linux/psi_types.h>
 
 #ifdef CONFIG_CGROUPS
 
@@ -424,6 +425,9 @@ struct cgroup {
 	/* used to schedule release agent */
 	struct work_struct release_agent_work;
 
+	/* used to track pressure stalls */
+	struct psi_group psi;
+
 	/* used to store eBPF programs */
 	struct cgroup_bpf bpf;
 
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 473e0c0abb86..fd94c294c207 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -627,6 +627,11 @@ static inline void pr_cont_cgroup_path(struct cgroup *cgrp)
 	pr_cont_kernfs_path(cgrp->kn);
 }
 
+static inline struct psi_group *cgroup_psi(struct cgroup *cgrp)
+{
+	return &cgrp->psi;
+}
+
 static inline void cgroup_init_kthreadd(void)
 {
 	/*
@@ -680,6 +685,16 @@ static inline union kernfs_node_id *cgroup_get_kernfs_id(struct cgroup *cgrp)
 	return NULL;
 }
 
+static inline struct cgroup *cgroup_parent(struct cgroup *cgrp)
+{
+	return NULL;
+}
+
+static inline struct psi_group *cgroup_psi(struct cgroup *cgrp)
+{
+	return NULL;
+}
+
 static inline bool task_under_cgroup_hierarchy(struct task_struct *task,
 					       struct cgroup *ancestor)
 {
diff --git a/include/linux/psi.h b/include/linux/psi.h
index 371af1479699..05c3dae3e9c5 100644
--- a/include/linux/psi.h
+++ b/include/linux/psi.h
@@ -4,6 +4,9 @@
 #include <linux/psi_types.h>
 #include <linux/sched.h>
 
+struct seq_file;
+struct css_set;
+
 #ifdef CONFIG_PSI
 
 extern bool psi_disabled;
@@ -15,6 +18,14 @@ void psi_task_change(struct task_struct *task, u64 now, int clear, int set);
 void psi_memstall_enter(unsigned long *flags);
 void psi_memstall_leave(unsigned long *flags);
 
+int psi_show(struct seq_file *s, struct psi_group *group, enum psi_res res);
+
+#ifdef CONFIG_CGROUPS
+int psi_cgroup_alloc(struct cgroup *cgrp);
+void psi_cgroup_free(struct cgroup *cgrp);
+void cgroup_move_task(struct task_struct *p, struct css_set *to);
+#endif
+
 #else /* CONFIG_PSI */
 
 static inline void psi_init(void) {}
@@ -22,6 +33,20 @@ static inline void psi_init(void) {}
 static inline void psi_memstall_enter(unsigned long *flags) {}
 static inline void psi_memstall_leave(unsigned long *flags) {}
 
+#ifdef CONFIG_CGROUPS
+static inline int psi_cgroup_alloc(struct cgroup *cgrp)
+{
+	return 0;
+}
+static inline void psi_cgroup_free(struct cgroup *cgrp)
+{
+}
+static inline void cgroup_move_task(struct task_struct *p, struct css_set *to)
+{
+	rcu_assign_pointer(p->cgroups, to);
+}
+#endif
+
 #endif /* CONFIG_PSI */
 
 #endif /* _LINUX_PSI_H */
diff --git a/init/Kconfig b/init/Kconfig
index ad61ddb5d68e..5c029f8d69f1 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -468,6 +468,10 @@ config PSI
 	  the share of walltime in which some or all tasks in the system are
 	  delayed due to contention of the respective resource.
 
+	  In kernels with cgroup support (cgroup2 only), cgroups will
+	  have cpu.pressure, memory.pressure, and io.pressure files,
+	  which aggregate pressure stalls for the grouped tasks only.
+
 	  For more details see Documentation/accounting/psi.txt.
 
 	  Say N if unsure.
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index a662bfcbea0e..bbb00b3ab752 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -54,6 +54,7 @@
 #include <linux/proc_ns.h>
 #include <linux/nsproxy.h>
 #include <linux/file.h>
+#include <linux/psi.h>
 #include <net/sock.h>
 
 #define CREATE_TRACE_POINTS
@@ -826,7 +827,7 @@ static void css_set_move_task(struct task_struct *task,
 		 */
 		WARN_ON_ONCE(task->flags & PF_EXITING);
 
-		rcu_assign_pointer(task->cgroups, to_cset);
+		cgroup_move_task(task, to_cset);
 		list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
 							     &to_cset->tasks);
 	}
@@ -3388,6 +3389,21 @@ static int cpu_stat_show(struct seq_file *seq, void *v)
 	return ret;
 }
 
+#ifdef CONFIG_PSI
+static int cgroup_io_pressure_show(struct seq_file *seq, void *v)
+{
+	return psi_show(seq, &seq_css(seq)->cgroup->psi, PSI_IO);
+}
+static int cgroup_memory_pressure_show(struct seq_file *seq, void *v)
+{
+	return psi_show(seq, &seq_css(seq)->cgroup->psi, PSI_MEM);
+}
+static int cgroup_cpu_pressure_show(struct seq_file *seq, void *v)
+{
+	return psi_show(seq, &seq_css(seq)->cgroup->psi, PSI_CPU);
+}
+#endif
+
 static int cgroup_file_open(struct kernfs_open_file *of)
 {
 	struct cftype *cft = of->kn->priv;
@@ -4499,6 +4515,23 @@ static struct cftype cgroup_base_files[] = {
 		.flags = CFTYPE_NOT_ON_ROOT,
 		.seq_show = cpu_stat_show,
 	},
+#ifdef CONFIG_PSI
+	{
+		.name = "io.pressure",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.seq_show = cgroup_io_pressure_show,
+	},
+	{
+		.name = "memory.pressure",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.seq_show = cgroup_memory_pressure_show,
+	},
+	{
+		.name = "cpu.pressure",
+		.flags = CFTYPE_NOT_ON_ROOT,
+		.seq_show = cgroup_cpu_pressure_show,
+	},
+#endif
 	{ }	/* terminate */
 };
 
@@ -4559,6 +4592,7 @@ static void css_free_rwork_fn(struct work_struct *work)
 			 */
 			cgroup_put(cgroup_parent(cgrp));
 			kernfs_put(cgrp->kn);
+			psi_cgroup_free(cgrp);
 			if (cgroup_on_dfl(cgrp))
 				cgroup_stat_exit(cgrp);
 			kfree(cgrp);
@@ -4805,10 +4839,15 @@ static struct cgroup *cgroup_create(struct cgroup *parent)
 	cgrp->self.parent = &parent->self;
 	cgrp->root = root;
 	cgrp->level = level;
-	ret = cgroup_bpf_inherit(cgrp);
+
+	ret = psi_cgroup_alloc(cgrp);
 	if (ret)
 		goto out_idr_free;
 
+	ret = cgroup_bpf_inherit(cgrp);
+	if (ret)
+		goto out_psi_free;
+
 	for (tcgrp = cgrp; tcgrp; tcgrp = cgroup_parent(tcgrp)) {
 		cgrp->ancestor_ids[tcgrp->level] = tcgrp->id;
 
@@ -4846,6 +4885,8 @@ static struct cgroup *cgroup_create(struct cgroup *parent)
 
 	return cgrp;
 
+out_psi_free:
+	psi_cgroup_free(cgrp);
 out_idr_free:
 	cgroup_idr_remove(&root->cgroup_idr, cgrp->id);
 out_stat_exit:
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 57ec86592b5a..a20f885da66f 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -464,6 +464,9 @@ static void psi_group_change(struct psi_group *group, int cpu, u64 now,
 
 void psi_task_change(struct task_struct *task, u64 now, int clear, int set)
 {
+#ifdef CONFIG_CGROUPS
+	struct cgroup *cgroup, *parent;
+#endif
 	int cpu = task_cpu(task);
 
 	if (psi_disabled)
@@ -485,6 +488,18 @@ void psi_task_change(struct task_struct *task, u64 now, int clear, int set)
 	task->psi_flags |= set;
 
 	psi_group_change(&psi_system, cpu, now, clear, set);
+
+#ifdef CONFIG_CGROUPS
+	cgroup = task->cgroups->dfl_cgrp;
+	while (cgroup && (parent = cgroup_parent(cgroup))) {
+		struct psi_group *group;
+
+		group = cgroup_psi(cgroup);
+		psi_group_change(group, cpu, now, clear, set);
+
+		cgroup = parent;
+	}
+#endif
 }
 
 /**
@@ -551,8 +566,70 @@ void psi_memstall_leave(unsigned long *flags)
 	rq_unlock_irq(rq, &rf);
 }
 
-static int psi_show(struct seq_file *m, struct psi_group *group,
-		    enum psi_res res)
+#ifdef CONFIG_CGROUPS
+int psi_cgroup_alloc(struct cgroup *cgroup)
+{
+	cgroup->psi.pcpu = alloc_percpu(struct psi_group_cpu);
+	if (!cgroup->psi.pcpu)
+		return -ENOMEM;
+	psi_group_init(&cgroup->psi);
+	return 0;
+}
+
+void psi_cgroup_free(struct cgroup *cgroup)
+{
+	cancel_delayed_work_sync(&cgroup->psi.clock_work);
+	free_percpu(cgroup->psi.pcpu);
+}
+
+/**
+ * cgroup_move_task - move task to a different cgroup
+ * @task: the task
+ * @to: the target css_set
+ *
+ * Move task to a new cgroup and safely migrate its associated stall
+ * state between the different groups.
+ *
+ * This function acquires the task's rq lock to lock out concurrent
+ * changes to the task's scheduling state and - in case the task is
+ * running - concurrent changes to its stall state.
+ */
+void cgroup_move_task(struct task_struct *task, struct css_set *to)
+{
+	unsigned int task_flags = 0;
+	struct rq_flags rf;
+	struct rq *rq;
+	u64 now;
+
+	rq = task_rq_lock(task, &rf);
+
+	if (task_on_rq_queued(task))
+		task_flags = TSK_RUNNING;
+	else if (task->in_iowait)
+		task_flags = TSK_IOWAIT;
+	if (task->flags & PF_MEMSTALL)
+		task_flags |= TSK_MEMSTALL;
+
+	if (task_flags) {
+		update_rq_clock(rq);
+		now = rq_clock(rq);
+		psi_task_change(task, now, task_flags, 0);
+	}
+
+	/*
+	 * Lame to do this here, but the scheduler cannot be locked
+	 * from the outside, so we move cgroups from inside sched/.
+	 */
+	rcu_assign_pointer(task->cgroups, to);
+
+	if (task_flags)
+		psi_task_change(task, now, 0, task_flags);
+
+	task_rq_unlock(rq, task, &rf);
+}
+#endif /* CONFIG_CGROUPS */
+
+int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
 {
 	int full;
 
-- 
2.18.0

Re: [PATCH 0/9] psi: pressure stall information for CPU, memory, and IO v3

[peter enderborg]

On 08/01/2018 05:19 PM, Johannes Weiner wrote:
>
> A kernel with CONFIG_PSI=y will create a /proc/pressure directory with
> 3 files: cpu, memory, and io. If using cgroup2, cgroups will also have
> cpu.pressure, memory.pressure and io.pressure files, which simply
> aggregate task stalls at the cgroup level instead of system-wide.
>
Usually there are objections to add more stuff to /proc. Is this an exception?

Re: [PATCH 0/9] psi: pressure stall information for CPU, memory, and IO v3

[Johannes Weiner]

On Tue, Aug 07, 2018 at 01:50:09PM +0200, peter enderborg wrote:
> On 08/01/2018 05:19 PM, Johannes Weiner wrote:
> >
> > A kernel with CONFIG_PSI=y will create a /proc/pressure directory with
> > 3 files: cpu, memory, and io. If using cgroup2, cgroups will also have
> > cpu.pressure, memory.pressure and io.pressure files, which simply
> > aggregate task stalls at the cgroup level instead of system-wide.
> >
> Usually there are objections to add more stuff to /proc. Is this an exception?

It seems like a good fit given that all other system stats of this
type and format are there: loadavg, schedstat, diskstats, uptime etc.

sysfs, and its concept of kernel objects and their attributes, doesn't
really match the type of info exported here. And its breakdown of
complex information into many directories and files can be kind of
tedious to be honest; some information is just more human readable in
a simple table, and still trivial to parse mechanically.

It would also be nice to keep the same file format for both the system
level and cgroups, to avoid having two separate presentations (and two
parsers) for the same type of information at different scopes, but the
sysfs design goals clash with the cgroupfs ones. If we exported the
system stats at the root cgroup level, we'd still need an interface
for !CGROUP systems, and having two ways of reading actually identical
data would again be fairly ugly.