Re: [patch 4/4] memcg: unify charge/uncharge quantities to units of pages

[Johannes Weiner <hannes@cmpxchg.org>]

The update to 1/4 made one hunk of this one no longer apply, so to
save you the hassle, here is a complete replacement.

What I changed to visibly break new old-API users:

1. mem_cgroup_margin: sufficiently new to not have new users
developped that assume the return value to be in unit of bytes, so I
left it alone

2. __mem_cgroup_do_charge: dropped the underscores

3. __mem_cgroup_try_charge: moved @nr_pages parameter so that using
the old function signature would complain about passing integers for
pointers and vice versa

4. __mem_cgroup_commit_charge: same as 3.

5. mem_cgroup_move_account: same as 4.

6. __do_uncharge: renamed to mem_cgroup_do_uncharge

---
From: Johannes Weiner <hannes@cmpxchg.org>
Subject: [patch] memcg: unify charge/uncharge quantities to units of pages

There is no clear pattern when we pass a page count and when we pass a
byte count that is a multiple of PAGE_SIZE.

We never charge or uncharge subpage quantities, so convert it all to
page counts.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 mm/memcontrol.c |  135 ++++++++++++++++++++++++++----------------------------
 1 files changed, 65 insertions(+), 70 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 63c65ab..78a79ea 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1092,16 +1092,16 @@ unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
  * @mem: the memory cgroup
  *
  * Returns the maximum amount of memory @mem can be charged with, in
- * bytes.
+ * pages.
  */
-static unsigned long long mem_cgroup_margin(struct mem_cgroup *mem)
+static unsigned long mem_cgroup_margin(struct mem_cgroup *mem)
 {
 	unsigned long long margin;
 
 	margin = res_counter_margin(&mem->res);
 	if (do_swap_account)
 		margin = min(margin, res_counter_margin(&mem->memsw));
-	return margin;
+	return margin >> PAGE_SHIFT;
 }
 
 static unsigned int get_swappiness(struct mem_cgroup *memcg)
@@ -1637,7 +1637,7 @@ EXPORT_SYMBOL(mem_cgroup_update_page_stat);
  * size of first charge trial. "32" comes from vmscan.c's magic value.
  * TODO: maybe necessary to use big numbers in big irons.
  */
-#define CHARGE_SIZE	(32 * PAGE_SIZE)
+#define CHARGE_BATCH	32U
 struct memcg_stock_pcp {
 	struct mem_cgroup *cached; /* this never be root cgroup */
 	unsigned int nr_pages;
@@ -1812,9 +1812,10 @@ enum {
 	CHARGE_OOM_DIE,		/* the current is killed because of OOM */
 };
 
-static int __mem_cgroup_do_charge(struct mem_cgroup *mem, gfp_t gfp_mask,
-				int csize, bool oom_check)
+static int mem_cgroup_do_charge(struct mem_cgroup *mem, gfp_t gfp_mask,
+				unsigned int nr_pages, bool oom_check)
 {
+	unsigned long csize = nr_pages * PAGE_SIZE;
 	struct mem_cgroup *mem_over_limit;
 	struct res_counter *fail_res;
 	unsigned long flags = 0;
@@ -1835,14 +1836,13 @@ static int __mem_cgroup_do_charge(struct mem_cgroup *mem, gfp_t gfp_mask,
 	} else
 		mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
 	/*
-	 * csize can be either a huge page (HPAGE_SIZE), a batch of
-	 * regular pages (CHARGE_SIZE), or a single regular page
-	 * (PAGE_SIZE).
+	 * nr_pages can be either a huge page (HPAGE_PMD_NR), a batch
+	 * of regular pages (CHARGE_BATCH), or a single regular page (1).
 	 *
 	 * Never reclaim on behalf of optional batching, retry with a
 	 * single page instead.
 	 */
-	if (csize == CHARGE_SIZE)
+	if (nr_pages == CHARGE_BATCH)
 		return CHARGE_RETRY;
 
 	if (!(gfp_mask & __GFP_WAIT))
@@ -1850,7 +1850,7 @@ static int __mem_cgroup_do_charge(struct mem_cgroup *mem, gfp_t gfp_mask,
 
 	ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, NULL,
 					      gfp_mask, flags);
-	if (mem_cgroup_margin(mem_over_limit) >= csize)
+	if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
 		return CHARGE_RETRY;
 	/*
 	 * Even though the limit is exceeded at this point, reclaim
@@ -1861,7 +1861,7 @@ static int __mem_cgroup_do_charge(struct mem_cgroup *mem, gfp_t gfp_mask,
 	 * unlikely to succeed so close to the limit, and we fall back
 	 * to regular pages anyway in case of failure.
 	 */
-	if (csize == PAGE_SIZE && ret)
+	if (nr_pages == 1 && ret)
 		return CHARGE_RETRY;
 
 	/*
@@ -1887,13 +1887,14 @@ static int __mem_cgroup_do_charge(struct mem_cgroup *mem, gfp_t gfp_mask,
  */
 static int __mem_cgroup_try_charge(struct mm_struct *mm,
 				   gfp_t gfp_mask,
-				   struct mem_cgroup **memcg, bool oom,
-				   int page_size)
+				   unsigned int nr_pages,
+				   struct mem_cgroup **memcg,
+				   bool oom)
 {
+	unsigned int batch = max(CHARGE_BATCH, nr_pages);
 	int nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
 	struct mem_cgroup *mem = NULL;
 	int ret;
-	int csize = max(CHARGE_SIZE, (unsigned long) page_size);
 
 	/*
 	 * Unlike gloval-vm's OOM-kill, we're not in memory shortage
@@ -1918,7 +1919,7 @@ again:
 		VM_BUG_ON(css_is_removed(&mem->css));
 		if (mem_cgroup_is_root(mem))
 			goto done;
-		if (page_size == PAGE_SIZE && consume_stock(mem))
+		if (nr_pages == 1 && consume_stock(mem))
 			goto done;
 		css_get(&mem->css);
 	} else {
@@ -1941,7 +1942,7 @@ again:
 			rcu_read_unlock();
 			goto done;
 		}
-		if (page_size == PAGE_SIZE && consume_stock(mem)) {
+		if (nr_pages == 1 && consume_stock(mem)) {
 			/*
 			 * It seems dagerous to access memcg without css_get().
 			 * But considering how consume_stok works, it's not
@@ -1976,13 +1977,12 @@ again:
 			nr_oom_retries = MEM_CGROUP_RECLAIM_RETRIES;
 		}
 
-		ret = __mem_cgroup_do_charge(mem, gfp_mask, csize, oom_check);
-
+		ret = mem_cgroup_do_charge(mem, gfp_mask, batch, oom_check);
 		switch (ret) {
 		case CHARGE_OK:
 			break;
 		case CHARGE_RETRY: /* not in OOM situation but retry */
-			csize = page_size;
+			batch = nr_pages;
 			css_put(&mem->css);
 			mem = NULL;
 			goto again;
@@ -2003,8 +2003,8 @@ again:
 		}
 	} while (ret != CHARGE_OK);
 
-	if (csize > page_size)
-		refill_stock(mem, (csize - page_size) >> PAGE_SHIFT);
+	if (batch > nr_pages)
+		refill_stock(mem, batch - nr_pages);
 	css_put(&mem->css);
 done:
 	*memcg = mem;
@@ -2083,12 +2083,10 @@ struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
 
 static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
 				       struct page *page,
+				       unsigned int nr_pages,
 				       struct page_cgroup *pc,
-				       enum charge_type ctype,
-				       int page_size)
+				       enum charge_type ctype)
 {
-	int nr_pages = page_size >> PAGE_SHIFT;
-
 	lock_page_cgroup(pc);
 	if (unlikely(PageCgroupUsed(pc))) {
 		unlock_page_cgroup(pc);
@@ -2177,26 +2175,28 @@ void mem_cgroup_split_huge_fixup(struct page *head, struct page *tail)
 /**
  * mem_cgroup_move_account - move account of the page
  * @page: the page
+ * @nr_pages: number of regular pages (>1 for huge pages)
  * @pc:	page_cgroup of the page.
  * @from: mem_cgroup which the page is moved from.
  * @to:	mem_cgroup which the page is moved to. @from != @to.
  * @uncharge: whether we should call uncharge and css_put against @from.
- * @charge_size: number of bytes to charge (regular or huge page)
  *
  * The caller must confirm following.
  * - page is not on LRU (isolate_page() is useful.)
- * - compound_lock is held when charge_size > PAGE_SIZE
+ * - compound_lock is held when nr_pages > 1
  *
  * This function doesn't do "charge" nor css_get to new cgroup. It should be
  * done by a caller(__mem_cgroup_try_charge would be usefull). If @uncharge is
  * true, this function does "uncharge" from old cgroup, but it doesn't if
  * @uncharge is false, so a caller should do "uncharge".
  */
-static int mem_cgroup_move_account(struct page *page, struct page_cgroup *pc,
-				   struct mem_cgroup *from, struct mem_cgroup *to,
-				   bool uncharge, int charge_size)
+static int mem_cgroup_move_account(struct page *page,
+				   unsigned int nr_pages,
+				   struct page_cgroup *pc,
+				   struct mem_cgroup *from,
+				   struct mem_cgroup *to,
+				   bool uncharge)
 {
-	int nr_pages = charge_size >> PAGE_SHIFT;
 	unsigned long flags;
 	int ret;
 
@@ -2209,7 +2209,7 @@ static int mem_cgroup_move_account(struct page *page, struct page_cgroup *pc,
 	 * hold it.
 	 */
 	ret = -EBUSY;
-	if (charge_size > PAGE_SIZE && !PageTransHuge(page))
+	if (nr_pages > 1 && !PageTransHuge(page))
 		goto out;
 
 	lock_page_cgroup(pc);
@@ -2267,7 +2267,7 @@ static int mem_cgroup_move_parent(struct page *page,
 	struct cgroup *cg = child->css.cgroup;
 	struct cgroup *pcg = cg->parent;
 	struct mem_cgroup *parent;
-	int page_size = PAGE_SIZE;
+	unsigned int nr_pages;
 	unsigned long flags;
 	int ret;
 
@@ -2281,23 +2281,21 @@ static int mem_cgroup_move_parent(struct page *page,
 	if (isolate_lru_page(page))
 		goto put;
 
-	if (PageTransHuge(page))
-		page_size = HPAGE_SIZE;
+	nr_pages = hpage_nr_pages(page);
 
 	parent = mem_cgroup_from_cont(pcg);
-	ret = __mem_cgroup_try_charge(NULL, gfp_mask,
-				&parent, false, page_size);
+	ret = __mem_cgroup_try_charge(NULL, gfp_mask, nr_pages, &parent, false);
 	if (ret || !parent)
 		goto put_back;
 
-	if (page_size > PAGE_SIZE)
+	if (nr_pages > 1)
 		flags = compound_lock_irqsave(page);
 
-	ret = mem_cgroup_move_account(page, pc, child, parent, true, page_size);
+	ret = mem_cgroup_move_account(page, nr_pages, pc, child, parent, true);
 	if (ret)
-		__mem_cgroup_cancel_charge(parent, page_size >> PAGE_SHIFT);
+		__mem_cgroup_cancel_charge(parent, nr_pages);
 
-	if (page_size > PAGE_SIZE)
+	if (nr_pages > 1)
 		compound_unlock_irqrestore(page, flags);
 put_back:
 	putback_lru_page(page);
@@ -2317,13 +2315,13 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
 				gfp_t gfp_mask, enum charge_type ctype)
 {
 	struct mem_cgroup *mem = NULL;
-	int page_size = PAGE_SIZE;
+	unsigned int nr_pages = 1;
 	struct page_cgroup *pc;
 	bool oom = true;
 	int ret;
 
 	if (PageTransHuge(page)) {
-		page_size <<= compound_order(page);
+		nr_pages <<= compound_order(page);
 		VM_BUG_ON(!PageTransHuge(page));
 		/*
 		 * Never OOM-kill a process for a huge page.  The
@@ -2335,11 +2333,11 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
 	pc = lookup_page_cgroup(page);
 	BUG_ON(!pc); /* XXX: remove this and move pc lookup into commit */
 
-	ret = __mem_cgroup_try_charge(mm, gfp_mask, &mem, oom, page_size);
+	ret = __mem_cgroup_try_charge(mm, gfp_mask, nr_pages, &mem, oom);
 	if (ret || !mem)
 		return ret;
 
-	__mem_cgroup_commit_charge(mem, page, pc, ctype, page_size);
+	__mem_cgroup_commit_charge(mem, page, nr_pages, pc, ctype);
 	return 0;
 }
 
@@ -2455,13 +2453,13 @@ int mem_cgroup_try_charge_swapin(struct mm_struct *mm,
 	if (!mem)
 		goto charge_cur_mm;
 	*ptr = mem;
-	ret = __mem_cgroup_try_charge(NULL, mask, ptr, true, PAGE_SIZE);
+	ret = __mem_cgroup_try_charge(NULL, mask, 1, ptr, true);
 	css_put(&mem->css);
 	return ret;
 charge_cur_mm:
 	if (unlikely(!mm))
 		mm = &init_mm;
-	return __mem_cgroup_try_charge(mm, mask, ptr, true, PAGE_SIZE);
+	return __mem_cgroup_try_charge(mm, mask, 1, ptr, true);
 }
 
 static void
@@ -2477,7 +2475,7 @@ __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr,
 	cgroup_exclude_rmdir(&ptr->css);
 	pc = lookup_page_cgroup(page);
 	mem_cgroup_lru_del_before_commit_swapcache(page);
-	__mem_cgroup_commit_charge(ptr, page, pc, ctype, PAGE_SIZE);
+	__mem_cgroup_commit_charge(ptr, page, 1, pc, ctype);
 	mem_cgroup_lru_add_after_commit_swapcache(page);
 	/*
 	 * Now swap is on-memory. This means this page may be
@@ -2529,12 +2527,13 @@ void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *mem)
 	__mem_cgroup_cancel_charge(mem, 1);
 }
 
-static void
-__do_uncharge(struct mem_cgroup *mem, const enum charge_type ctype,
-	      int page_size)
+static void mem_cgroup_do_uncharge(struct mem_cgroup *mem,
+				   unsigned int nr_pages,
+				   const enum charge_type ctype)
 {
 	struct memcg_batch_info *batch = NULL;
 	bool uncharge_memsw = true;
+
 	/* If swapout, usage of swap doesn't decrease */
 	if (!do_swap_account || ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
 		uncharge_memsw = false;
@@ -2558,7 +2557,7 @@ __do_uncharge(struct mem_cgroup *mem, const enum charge_type ctype,
 	if (!batch->do_batch || test_thread_flag(TIF_MEMDIE))
 		goto direct_uncharge;
 
-	if (page_size != PAGE_SIZE)
+	if (nr_pages > 1)
 		goto direct_uncharge;
 
 	/*
@@ -2574,9 +2573,9 @@ __do_uncharge(struct mem_cgroup *mem, const enum charge_type ctype,
 		batch->memsw_nr_pages++;
 	return;
 direct_uncharge:
-	res_counter_uncharge(&mem->res, page_size);
+	res_counter_uncharge(&mem->res, nr_pages * PAGE_SIZE);
 	if (uncharge_memsw)
-		res_counter_uncharge(&mem->memsw, page_size);
+		res_counter_uncharge(&mem->memsw, nr_pages * PAGE_SIZE);
 	if (unlikely(batch->memcg != mem))
 		memcg_oom_recover(mem);
 	return;
@@ -2588,10 +2587,9 @@ direct_uncharge:
 static struct mem_cgroup *
 __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
 {
-	int count;
-	struct page_cgroup *pc;
 	struct mem_cgroup *mem = NULL;
-	int page_size = PAGE_SIZE;
+	unsigned int nr_pages = 1;
+	struct page_cgroup *pc;
 
 	if (mem_cgroup_disabled())
 		return NULL;
@@ -2600,11 +2598,9 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
 		return NULL;
 
 	if (PageTransHuge(page)) {
-		page_size <<= compound_order(page);
+		nr_pages <<= compound_order(page);
 		VM_BUG_ON(!PageTransHuge(page));
 	}
-
-	count = page_size >> PAGE_SHIFT;
 	/*
 	 * Check if our page_cgroup is valid
 	 */
@@ -2637,7 +2633,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
 		break;
 	}
 
-	mem_cgroup_charge_statistics(mem, PageCgroupCache(pc), -count);
+	mem_cgroup_charge_statistics(mem, PageCgroupCache(pc), -nr_pages);
 
 	ClearPageCgroupUsed(pc);
 	/*
@@ -2658,7 +2654,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
 		mem_cgroup_get(mem);
 	}
 	if (!mem_cgroup_is_root(mem))
-		__do_uncharge(mem, ctype, page_size);
+		mem_cgroup_do_uncharge(mem, nr_pages, ctype);
 
 	return mem;
 
@@ -2850,8 +2846,8 @@ static inline int mem_cgroup_move_swap_account(swp_entry_t entry,
 int mem_cgroup_prepare_migration(struct page *page,
 	struct page *newpage, struct mem_cgroup **ptr, gfp_t gfp_mask)
 {
-	struct page_cgroup *pc;
 	struct mem_cgroup *mem = NULL;
+	struct page_cgroup *pc;
 	enum charge_type ctype;
 	int ret = 0;
 
@@ -2907,7 +2903,7 @@ int mem_cgroup_prepare_migration(struct page *page,
 		return 0;
 
 	*ptr = mem;
-	ret = __mem_cgroup_try_charge(NULL, gfp_mask, ptr, false, PAGE_SIZE);
+	ret = __mem_cgroup_try_charge(NULL, gfp_mask, 1, ptr, false);
 	css_put(&mem->css);/* drop extra refcnt */
 	if (ret || *ptr == NULL) {
 		if (PageAnon(page)) {
@@ -2934,7 +2930,7 @@ int mem_cgroup_prepare_migration(struct page *page,
 		ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
 	else
 		ctype = MEM_CGROUP_CHARGE_TYPE_SHMEM;
-	__mem_cgroup_commit_charge(mem, page, pc, ctype, PAGE_SIZE);
+	__mem_cgroup_commit_charge(mem, page, 1, pc, ctype);
 	return ret;
 }
 
@@ -4591,8 +4587,7 @@ one_by_one:
 			batch_count = PRECHARGE_COUNT_AT_ONCE;
 			cond_resched();
 		}
-		ret = __mem_cgroup_try_charge(NULL, GFP_KERNEL, &mem, false,
-					      PAGE_SIZE);
+		ret = __mem_cgroup_try_charge(NULL, GFP_KERNEL, 1, &mem, false);
 		if (ret || !mem)
 			/* mem_cgroup_clear_mc() will do uncharge later */
 			return -ENOMEM;
@@ -4937,8 +4932,8 @@ retry:
 			if (isolate_lru_page(page))
 				goto put;
 			pc = lookup_page_cgroup(page);
-			if (!mem_cgroup_move_account(page, pc,
-					mc.from, mc.to, false, PAGE_SIZE)) {
+			if (!mem_cgroup_move_account(page, 1, pc,
+						     mc.from, mc.to, false)) {
 				mc.precharge--;
 				/* we uncharge from mc.from later. */
 				mc.moved_charge++;
-- 
1.7.4