[PATCH -mm -v6 2/9] mm, memcg: Support to charge/uncharge multiple swap entries

[PATCH -mm -v6 2/9] mm, memcg: Support to charge/uncharge multiple swap entries

[Huang, Ying]

From: Huang Ying <ying.huang@intel.com>

This patch make it possible to charge or uncharge a set of continuous
swap entries in the swap cgroup.  The number of swap entries is
specified via an added parameter.

This will be used for the THP (Transparent Huge Page) swap support.
Where a swap cluster backing a THP may be allocated and freed as a
whole.  So a set of (HPAGE_PMD_NR) continuous swap entries backing one
THP need to be charged or uncharged together.  This will batch the
cgroup operations for the THP swap too.

Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: cgroups@vger.kernel.org
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
---
 include/linux/swap.h        | 12 ++++++----
 include/linux/swap_cgroup.h |  6 +++--
 mm/memcontrol.c             | 57 +++++++++++++++++++++++++--------------------
 mm/shmem.c                  |  2 +-
 mm/swap_cgroup.c            | 40 +++++++++++++++++++++++--------
 mm/swap_state.c             |  2 +-
 mm/swapfile.c               |  2 +-
 7 files changed, 77 insertions(+), 44 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 486494e6b2fc..278e1349a424 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -550,8 +550,10 @@ static inline int mem_cgroup_swappiness(struct mem_cgroup *mem)
 
 #ifdef CONFIG_MEMCG_SWAP
 extern void mem_cgroup_swapout(struct page *page, swp_entry_t entry);
-extern int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry);
-extern void mem_cgroup_uncharge_swap(swp_entry_t entry);
+extern int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry,
+				      unsigned int nr_entries);
+extern void mem_cgroup_uncharge_swap(swp_entry_t entry,
+				     unsigned int nr_entries);
 extern long mem_cgroup_get_nr_swap_pages(struct mem_cgroup *memcg);
 extern bool mem_cgroup_swap_full(struct page *page);
 #else
@@ -560,12 +562,14 @@ static inline void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 }
 
 static inline int mem_cgroup_try_charge_swap(struct page *page,
-					     swp_entry_t entry)
+					     swp_entry_t entry,
+					     unsigned int nr_entries)
 {
 	return 0;
 }
 
-static inline void mem_cgroup_uncharge_swap(swp_entry_t entry)
+static inline void mem_cgroup_uncharge_swap(swp_entry_t entry,
+					    unsigned int nr_entries)
 {
 }
 
diff --git a/include/linux/swap_cgroup.h b/include/linux/swap_cgroup.h
index 145306bdc92f..b2b8ec7bda3f 100644
--- a/include/linux/swap_cgroup.h
+++ b/include/linux/swap_cgroup.h
@@ -7,7 +7,8 @@
 
 extern unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
 					unsigned short old, unsigned short new);
-extern unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id);
+extern unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id,
+					 unsigned int nr_ents);
 extern unsigned short lookup_swap_cgroup_id(swp_entry_t ent);
 extern int swap_cgroup_swapon(int type, unsigned long max_pages);
 extern void swap_cgroup_swapoff(int type);
@@ -15,7 +16,8 @@ extern void swap_cgroup_swapoff(int type);
 #else
 
 static inline
-unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
+unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id,
+				  unsigned int nr_ents)
 {
 	return 0;
 }
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 537362e4108e..2b0b6012ad22 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2393,10 +2393,9 @@ void mem_cgroup_split_huge_fixup(struct page *head)
 
 #ifdef CONFIG_MEMCG_SWAP
 static void mem_cgroup_swap_statistics(struct mem_cgroup *memcg,
-					 bool charge)
+				       int nr_entries)
 {
-	int val = (charge) ? 1 : -1;
-	this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_SWAP], val);
+	this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_SWAP], nr_entries);
 }
 
 /**
@@ -2422,8 +2421,8 @@ static int mem_cgroup_move_swap_account(swp_entry_t entry,
 	new_id = mem_cgroup_id(to);
 
 	if (swap_cgroup_cmpxchg(entry, old_id, new_id) == old_id) {
-		mem_cgroup_swap_statistics(from, false);
-		mem_cgroup_swap_statistics(to, true);
+		mem_cgroup_swap_statistics(from, -1);
+		mem_cgroup_swap_statistics(to, 1);
 		return 0;
 	}
 	return -EINVAL;
@@ -5446,7 +5445,7 @@ void mem_cgroup_commit_charge(struct page *page, struct mem_cgroup *memcg,
 		 * let's not wait for it.  The page already received a
 		 * memory+swap charge, drop the swap entry duplicate.
 		 */
-		mem_cgroup_uncharge_swap(entry);
+		mem_cgroup_uncharge_swap(entry, nr_pages);
 	}
 }
 
@@ -5874,9 +5873,9 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 	 * ancestor for the swap instead and transfer the memory+swap charge.
 	 */
 	swap_memcg = mem_cgroup_id_get_online(memcg);
-	oldid = swap_cgroup_record(entry, mem_cgroup_id(swap_memcg));
+	oldid = swap_cgroup_record(entry, mem_cgroup_id(swap_memcg), 1);
 	VM_BUG_ON_PAGE(oldid, page);
-	mem_cgroup_swap_statistics(swap_memcg, true);
+	mem_cgroup_swap_statistics(swap_memcg, 1);
 
 	page->mem_cgroup = NULL;
 
@@ -5903,16 +5902,19 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 		css_put(&memcg->css);
 }
 
-/*
- * mem_cgroup_try_charge_swap - try charging a swap entry
+/**
+ * mem_cgroup_try_charge_swap - try charging a set of swap entries
  * @page: page being added to swap
- * @entry: swap entry to charge
+ * @entry: the first swap entry to charge
+ * @nr_entries: the number of swap entries to charge
  *
- * Try to charge @entry to the memcg that @page belongs to.
+ * Try to charge @nr_entries swap entries starting from @entry to the
+ * memcg that @page belongs to.
  *
  * Returns 0 on success, -ENOMEM on failure.
  */
-int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
+int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry,
+			       unsigned int nr_entries)
 {
 	struct mem_cgroup *memcg;
 	struct page_counter *counter;
@@ -5930,25 +5932,29 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
 	memcg = mem_cgroup_id_get_online(memcg);
 
 	if (!mem_cgroup_is_root(memcg) &&
-	    !page_counter_try_charge(&memcg->swap, 1, &counter)) {
+	    !page_counter_try_charge(&memcg->swap, nr_entries, &counter)) {
 		mem_cgroup_id_put(memcg);
 		return -ENOMEM;
 	}
 
-	oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg));
+	if (nr_entries > 1)
+		mem_cgroup_id_get_many(memcg, nr_entries - 1);
+	oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg), nr_entries);
 	VM_BUG_ON_PAGE(oldid, page);
-	mem_cgroup_swap_statistics(memcg, true);
+	mem_cgroup_swap_statistics(memcg, nr_entries);
 
 	return 0;
 }
 
 /**
- * mem_cgroup_uncharge_swap - uncharge a swap entry
- * @entry: swap entry to uncharge
+ * mem_cgroup_uncharge_swap - uncharge a set of swap entries
+ * @entry: the first swap entry to uncharge
+ * @nr_entries: the number of swap entries to uncharge
  *
- * Drop the swap charge associated with @entry.
+ * Drop the swap charge associated with @nr_entries swap entries
+ * starting from @entry.
  */
-void mem_cgroup_uncharge_swap(swp_entry_t entry)
+void mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_entries)
 {
 	struct mem_cgroup *memcg;
 	unsigned short id;
@@ -5956,18 +5962,19 @@ void mem_cgroup_uncharge_swap(swp_entry_t entry)
 	if (!do_swap_account)
 		return;
 
-	id = swap_cgroup_record(entry, 0);
+	id = swap_cgroup_record(entry, 0, nr_entries);
 	rcu_read_lock();
 	memcg = mem_cgroup_from_id(id);
 	if (memcg) {
 		if (!mem_cgroup_is_root(memcg)) {
 			if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
-				page_counter_uncharge(&memcg->swap, 1);
+				page_counter_uncharge(&memcg->swap, nr_entries);
 			else
-				page_counter_uncharge(&memcg->memsw, 1);
+				page_counter_uncharge(&memcg->memsw,
+						      nr_entries);
 		}
-		mem_cgroup_swap_statistics(memcg, false);
-		mem_cgroup_id_put(memcg);
+		mem_cgroup_swap_statistics(memcg, -nr_entries);
+		mem_cgroup_id_put_many(memcg, nr_entries);
 	}
 	rcu_read_unlock();
 }
diff --git a/mm/shmem.c b/mm/shmem.c
index e67d6ba4e98e..effe07ef5c26 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1294,7 +1294,7 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
 	if (!swap.val)
 		goto redirty;
 
-	if (mem_cgroup_try_charge_swap(page, swap))
+	if (mem_cgroup_try_charge_swap(page, swap, 1))
 		goto free_swap;
 
 	/*
diff --git a/mm/swap_cgroup.c b/mm/swap_cgroup.c
index 310ac0b8f974..8cee2d125815 100644
--- a/mm/swap_cgroup.c
+++ b/mm/swap_cgroup.c
@@ -58,21 +58,27 @@ static int swap_cgroup_prepare(int type)
 	return -ENOMEM;
 }
 
+static struct swap_cgroup *__lookup_swap_cgroup(struct swap_cgroup_ctrl *ctrl,
+						pgoff_t offset)
+{
+	struct page *mappage;
+	struct swap_cgroup *sc;
+
+	mappage = ctrl->map[offset / SC_PER_PAGE];
+	sc = page_address(mappage);
+	return sc + offset % SC_PER_PAGE;
+}
+
 static struct swap_cgroup *lookup_swap_cgroup(swp_entry_t ent,
 					struct swap_cgroup_ctrl **ctrlp)
 {
 	pgoff_t offset = swp_offset(ent);
 	struct swap_cgroup_ctrl *ctrl;
-	struct page *mappage;
-	struct swap_cgroup *sc;
 
 	ctrl = &swap_cgroup_ctrl[swp_type(ent)];
 	if (ctrlp)
 		*ctrlp = ctrl;
-
-	mappage = ctrl->map[offset / SC_PER_PAGE];
-	sc = page_address(mappage);
-	return sc + offset % SC_PER_PAGE;
+	return __lookup_swap_cgroup(ctrl, offset);
 }
 
 /**
@@ -105,25 +111,39 @@ unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
 }
 
 /**
- * swap_cgroup_record - record mem_cgroup for this swp_entry.
- * @ent: swap entry to be recorded into
+ * swap_cgroup_record - record mem_cgroup for a set of swap entries
+ * @ent: the first swap entry to be recorded into
  * @id: mem_cgroup to be recorded
+ * @nr_ents: number of swap entries to be recorded
  *
  * Returns old value at success, 0 at failure.
  * (Of course, old value can be 0.)
  */
-unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
+unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id,
+				  unsigned int nr_ents)
 {
 	struct swap_cgroup_ctrl *ctrl;
 	struct swap_cgroup *sc;
 	unsigned short old;
 	unsigned long flags;
+	pgoff_t offset = swp_offset(ent);
+	pgoff_t end = offset + nr_ents;
 
 	sc = lookup_swap_cgroup(ent, &ctrl);
 
 	spin_lock_irqsave(&ctrl->lock, flags);
 	old = sc->id;
-	sc->id = id;
+	for (;;) {
+		VM_BUG_ON(sc->id != old);
+		sc->id = id;
+		offset++;
+		if (offset == end)
+			break;
+		if (offset % SC_PER_PAGE)
+			sc++;
+		else
+			sc = __lookup_swap_cgroup(ctrl, offset);
+	}
 	spin_unlock_irqrestore(&ctrl->lock, flags);
 
 	return old;
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 473b71e052a8..3c248f0a0abc 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -182,7 +182,7 @@ int add_to_swap(struct page *page, struct list_head *list)
 	if (!entry.val)
 		return 0;
 
-	if (mem_cgroup_try_charge_swap(page, entry)) {
+	if (mem_cgroup_try_charge_swap(page, entry, 1)) {
 		swapcache_free(entry);
 		return 0;
 	}
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 2396e1a350c8..a744604384ff 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1012,7 +1012,7 @@ static void swap_entry_free(struct swap_info_struct *p, swp_entry_t entry)
 	dec_cluster_info_page(p, p->cluster_info, offset);
 	unlock_cluster(ci);
 
-	mem_cgroup_uncharge_swap(entry);
+	mem_cgroup_uncharge_swap(entry, 1);
 	if (offset < p->lowest_bit)
 		p->lowest_bit = offset;
 	if (offset > p->highest_bit) {
-- 
2.11.0

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Re: [PATCH -mm -v6 2/9] mm, memcg: Support to charge/uncharge multiple swap entries

[Balbir Singh]

On Wed, 2017-03-08 at 15:26 +0800, Huang, Ying wrote:
> From: Huang Ying <ying.huang@intel.com>
> 
> This patch make it possible to charge or uncharge a set of continuous
> swap entries in the swap cgroup.  The number of swap entries is
> specified via an added parameter.
> 
> This will be used for the THP (Transparent Huge Page) swap support.
> Where a swap cluster backing a THP may be allocated and freed as a
> whole.  So a set of (HPAGE_PMD_NR) continuous swap entries backing one
> THP need to be charged or uncharged together.  This will batch the
> cgroup operations for the THP swap too.

A quick look at the patches makes it look sane. I wonder if we would
make sense to track THP swapout separately as well
(from a memory.stat perspective)

Balbir Singh

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Re: [PATCH -mm -v6 2/9] mm, memcg: Support to charge/uncharge multiple swap entries

[Huang, Ying]

Balbir Singh <bsingharora@gmail.com> writes:

> On Wed, 2017-03-08 at 15:26 +0800, Huang, Ying wrote:
>> From: Huang Ying <ying.huang@intel.com>
>> 
>> This patch make it possible to charge or uncharge a set of continuous
>> swap entries in the swap cgroup.  The number of swap entries is
>> specified via an added parameter.
>> 
>> This will be used for the THP (Transparent Huge Page) swap support.
>> Where a swap cluster backing a THP may be allocated and freed as a
>> whole.  So a set of (HPAGE_PMD_NR) continuous swap entries backing one
>> THP need to be charged or uncharged together.  This will batch the
>> cgroup operations for the THP swap too.
>
> A quick look at the patches makes it look sane. I wonder if we would
> make sense to track THP swapout separately as well
> (from a memory.stat perspective)

The patchset is just the first step of THP swap optimization.  So the
THP will still be split after putting the THP into the swap cache.  This
makes it unnecessary to change mem_cgroup_swapout().  I am working on a
following up patchset to further delaying THP splitting after swapping
out the THP to the disk.  In that patchset, I will change
mem_cgroup_swapout() too.

Best Regards,
Huang, Ying

> Balbir Singh

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Re: [PATCH -mm -v6 2/9] mm, memcg: Support to charge/uncharge multiple swap entries

[Balbir Singh]

On Thu, Mar 9, 2017 at 12:28 PM, Huang, Ying <ying.huang@intel.com> wrote:
> Balbir Singh <bsingharora@gmail.com> writes:
>
>> On Wed, 2017-03-08 at 15:26 +0800, Huang, Ying wrote:
>>> From: Huang Ying <ying.huang@intel.com>
>>>
>>> This patch make it possible to charge or uncharge a set of continuous
>>> swap entries in the swap cgroup.  The number of swap entries is
>>> specified via an added parameter.
>>>
>>> This will be used for the THP (Transparent Huge Page) swap support.
>>> Where a swap cluster backing a THP may be allocated and freed as a
>>> whole.  So a set of (HPAGE_PMD_NR) continuous swap entries backing one
>>> THP need to be charged or uncharged together.  This will batch the
>>> cgroup operations for the THP swap too.
>>
>> A quick look at the patches makes it look sane. I wonder if we would
>> make sense to track THP swapout separately as well
>> (from a memory.stat perspective)
>
> The patchset is just the first step of THP swap optimization.  So the
> THP will still be split after putting the THP into the swap cache.  This
> makes it unnecessary to change mem_cgroup_swapout().  I am working on a
> following up patchset to further delaying THP splitting after swapping
> out the THP to the disk.  In that patchset, I will change
> mem_cgroup_swapout() too.


Fair enough

Thanks,
Balbir

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