mm: embed the memcg pointer directly into struct page

Memory cgroups used to have 5 per-page pointers.  To allow users to
disable that amount of overhead during runtime, those pointers were
allocated in a separate array, with a translation layer between them and
struct page.

There is now only one page pointer remaining: the memcg pointer, that
indicates which cgroup the page is associated with when charged.  The
complexity of runtime allocation and the runtime translation overhead is
no longer justified to save that *potential* 0.19% of memory.  With
CONFIG_SLUB, page->mem_cgroup actually sits in the doubleword padding
after the page->private member and doesn't even increase struct page,
and then this patch actually saves space.  Remaining users that care can
still compile their kernels without CONFIG_MEMCG.

     text    data     bss     dec     hex     filename
  8828345 1725264  983040 11536649 b00909  vmlinux.old
  8827425 1725264  966656 11519345 afc571  vmlinux.new

[mhocko@suse.cz: update Documentation/cgroups/memory.txt]
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Vladimir Davydov <vdavydov@parallels.com>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Konstantin Khlebnikov <koct9i@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 35 insertions, 89 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 78cb3b05a9f..b864067791d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1274,7 +1274,6 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct zone *zone)
 {
 	struct mem_cgroup_per_zone *mz;
 	struct mem_cgroup *memcg;
-	struct page_cgroup *pc;
 	struct lruvec *lruvec;
 
 	if (mem_cgroup_disabled()) {
@@ -1282,8 +1281,7 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct zone *zone)
 		goto out;
 	}
 
-	pc = lookup_page_cgroup(page);
-	memcg = pc->mem_cgroup;
+	memcg = page->mem_cgroup;
 	/*
 	 * Swapcache readahead pages are added to the LRU - and
 	 * possibly migrated - before they are charged.
@@ -2020,16 +2018,13 @@ struct mem_cgroup *mem_cgroup_begin_page_stat(struct page *page,
 					      unsigned long *flags)
 {
 	struct mem_cgroup *memcg;
-	struct page_cgroup *pc;
 
 	rcu_read_lock();
 
 	if (mem_cgroup_disabled())
 		return NULL;
-
-	pc = lookup_page_cgroup(page);
 again:
-	memcg = pc->mem_cgroup;
+	memcg = page->mem_cgroup;
 	if (unlikely(!memcg))
 		return NULL;
 
@@ -2038,7 +2033,7 @@ again:
 		return memcg;
 
 	spin_lock_irqsave(&memcg->move_lock, *flags);
-	if (memcg != pc->mem_cgroup) {
+	if (memcg != page->mem_cgroup) {
 		spin_unlock_irqrestore(&memcg->move_lock, *flags);
 		goto again;
 	}
@@ -2405,15 +2400,12 @@ static struct mem_cgroup *mem_cgroup_lookup(unsigned short id)
 struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
 {
 	struct mem_cgroup *memcg;
-	struct page_cgroup *pc;
 	unsigned short id;
 	swp_entry_t ent;
 
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 
-	pc = lookup_page_cgroup(page);
-	memcg = pc->mem_cgroup;
-
+	memcg = page->mem_cgroup;
 	if (memcg) {
 		if (!css_tryget_online(&memcg->css))
 			memcg = NULL;
@@ -2463,10 +2455,9 @@ static void unlock_page_lru(struct page *page, int isolated)
 static void commit_charge(struct page *page, struct mem_cgroup *memcg,
 			  bool lrucare)
 {
-	struct page_cgroup *pc = lookup_page_cgroup(page);
 	int isolated;
 
-	VM_BUG_ON_PAGE(pc->mem_cgroup, page);
+	VM_BUG_ON_PAGE(page->mem_cgroup, page);
 
 	/*
 	 * In some cases, SwapCache and FUSE(splice_buf->radixtree), the page
@@ -2477,7 +2468,7 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg,
 
 	/*
 	 * Nobody should be changing or seriously looking at
-	 * pc->mem_cgroup at this point:
+	 * page->mem_cgroup at this point:
 	 *
 	 * - the page is uncharged
 	 *
@@ -2489,7 +2480,7 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg,
 	 * - a page cache insertion, a swapin fault, or a migration
 	 *   have the page locked
 	 */
-	pc->mem_cgroup = memcg;
+	page->mem_cgroup = memcg;
 
 	if (lrucare)
 		unlock_page_lru(page, isolated);
@@ -2972,8 +2963,6 @@ __memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **_memcg, int order)
 void __memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg,
 			      int order)
 {
-	struct page_cgroup *pc;
-
 	VM_BUG_ON(mem_cgroup_is_root(memcg));
 
 	/* The page allocation failed. Revert */
@@ -2981,14 +2970,12 @@ void __memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg,
 		memcg_uncharge_kmem(memcg, 1 << order);
 		return;
 	}
-	pc = lookup_page_cgroup(page);
-	pc->mem_cgroup = memcg;
+	page->mem_cgroup = memcg;
 }
 
 void __memcg_kmem_uncharge_pages(struct page *page, int order)
 {
-	struct page_cgroup *pc = lookup_page_cgroup(page);
-	struct mem_cgroup *memcg = pc->mem_cgroup;
+	struct mem_cgroup *memcg = page->mem_cgroup;
 
 	if (!memcg)
 		return;
@@ -2996,7 +2983,7 @@ void __memcg_kmem_uncharge_pages(struct page *page, int order)
 	VM_BUG_ON_PAGE(mem_cgroup_is_root(memcg), page);
 
 	memcg_uncharge_kmem(memcg, 1 << order);
-	pc->mem_cgroup = NULL;
+	page->mem_cgroup = NULL;
 }
 #else
 static inline void memcg_unregister_all_caches(struct mem_cgroup *memcg)
@@ -3014,16 +3001,15 @@ static inline void memcg_unregister_all_caches(struct mem_cgroup *memcg)
  */
 void mem_cgroup_split_huge_fixup(struct page *head)
 {
-	struct page_cgroup *pc = lookup_page_cgroup(head);
 	int i;
 
 	if (mem_cgroup_disabled())
 		return;
 
 	for (i = 1; i < HPAGE_PMD_NR; i++)
-		pc[i].mem_cgroup = pc[0].mem_cgroup;
+		head[i].mem_cgroup = head->mem_cgroup;
 
-	__this_cpu_sub(pc[0].mem_cgroup->stat->count[MEM_CGROUP_STAT_RSS_HUGE],
+	__this_cpu_sub(head->mem_cgroup->stat->count[MEM_CGROUP_STAT_RSS_HUGE],
 		       HPAGE_PMD_NR);
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
@@ -3032,7 +3018,6 @@ void mem_cgroup_split_huge_fixup(struct page *head)
  * 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.
  *
@@ -3045,7 +3030,6 @@ void mem_cgroup_split_huge_fixup(struct page *head)
  */
 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)
 {
@@ -3065,7 +3049,7 @@ static int mem_cgroup_move_account(struct page *page,
 		goto out;
 
 	/*
-	 * Prevent mem_cgroup_migrate() from looking at pc->mem_cgroup
+	 * Prevent mem_cgroup_migrate() from looking at page->mem_cgroup
 	 * of its source page while we change it: page migration takes
 	 * both pages off the LRU, but page cache replacement doesn't.
 	 */
@@ -3073,7 +3057,7 @@ static int mem_cgroup_move_account(struct page *page,
 		goto out;
 
 	ret = -EINVAL;
-	if (pc->mem_cgroup != from)
+	if (page->mem_cgroup != from)
 		goto out_unlock;
 
 	spin_lock_irqsave(&from->move_lock, flags);
@@ -3093,13 +3077,13 @@ static int mem_cgroup_move_account(struct page *page,
 	}
 
 	/*
-	 * It is safe to change pc->mem_cgroup here because the page
+	 * It is safe to change page->mem_cgroup here because the page
 	 * is referenced, charged, and isolated - we can't race with
 	 * uncharging, charging, migration, or LRU putback.
 	 */
 
 	/* caller should have done css_get */
-	pc->mem_cgroup = to;
+	page->mem_cgroup = to;
 	spin_unlock_irqrestore(&from->move_lock, flags);
 
 	ret = 0;
@@ -3174,36 +3158,17 @@ static inline int mem_cgroup_move_swap_account(swp_entry_t entry,
 #endif
 
 #ifdef CONFIG_DEBUG_VM
-static struct page_cgroup *lookup_page_cgroup_used(struct page *page)
-{
-	struct page_cgroup *pc;
-
-	pc = lookup_page_cgroup(page);
-	/*
-	 * Can be NULL while feeding pages into the page allocator for
-	 * the first time, i.e. during boot or memory hotplug;
-	 * or when mem_cgroup_disabled().
-	 */
-	if (likely(pc) && pc->mem_cgroup)
-		return pc;
-	return NULL;
-}
-
 bool mem_cgroup_bad_page_check(struct page *page)
 {
 	if (mem_cgroup_disabled())
 		return false;
 
-	return lookup_page_cgroup_used(page) != NULL;
+	return page->mem_cgroup != NULL;
 }
 
 void mem_cgroup_print_bad_page(struct page *page)
 {
-	struct page_cgroup *pc;
-
-	pc = lookup_page_cgroup_used(page);
-	if (pc)
-		pr_alert("pc:%p pc->mem_cgroup:%p\n", pc, pc->mem_cgroup);
+	pr_alert("page->mem_cgroup:%p\n", page->mem_cgroup);
 }
 #endif
 
@@ -5123,7 +5088,6 @@ static enum mc_target_type get_mctgt_type(struct vm_area_struct *vma,
 		unsigned long addr, pte_t ptent, union mc_target *target)
 {
 	struct page *page = NULL;
-	struct page_cgroup *pc;
 	enum mc_target_type ret = MC_TARGET_NONE;
 	swp_entry_t ent = { .val = 0 };
 
@@ -5137,13 +5101,12 @@ static enum mc_target_type get_mctgt_type(struct vm_area_struct *vma,
 	if (!page && !ent.val)
 		return ret;
 	if (page) {
-		pc = lookup_page_cgroup(page);
 		/*
 		 * Do only loose check w/o serialization.
-		 * mem_cgroup_move_account() checks the pc is valid or
+		 * mem_cgroup_move_account() checks the page is valid or
 		 * not under LRU exclusion.
 		 */
-		if (pc->mem_cgroup == mc.from) {
+		if (page->mem_cgroup == mc.from) {
 			ret = MC_TARGET_PAGE;
 			if (target)
 				target->page = page;
@@ -5171,15 +5134,13 @@ static enum mc_target_type get_mctgt_type_thp(struct vm_area_struct *vma,
 		unsigned long addr, pmd_t pmd, union mc_target *target)
 {
 	struct page *page = NULL;
-	struct page_cgroup *pc;
 	enum mc_target_type ret = MC_TARGET_NONE;
 
 	page = pmd_page(pmd);
 	VM_BUG_ON_PAGE(!page || !PageHead(page), page);
 	if (!move_anon())
 		return ret;
-	pc = lookup_page_cgroup(page);
-	if (pc->mem_cgroup == mc.from) {
+	if (page->mem_cgroup == mc.from) {
 		ret = MC_TARGET_PAGE;
 		if (target) {
 			get_page(page);
@@ -5378,7 +5339,6 @@ static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
 	enum mc_target_type target_type;
 	union mc_target target;
 	struct page *page;
-	struct page_cgroup *pc;
 
 	/*
 	 * We don't take compound_lock() here but no race with splitting thp
@@ -5399,9 +5359,8 @@ static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
 		if (target_type == MC_TARGET_PAGE) {
 			page = target.page;
 			if (!isolate_lru_page(page)) {
-				pc = lookup_page_cgroup(page);
 				if (!mem_cgroup_move_account(page, HPAGE_PMD_NR,
-							pc, mc.from, mc.to)) {
+							     mc.from, mc.to)) {
 					mc.precharge -= HPAGE_PMD_NR;
 					mc.moved_charge += HPAGE_PMD_NR;
 				}
@@ -5429,9 +5388,7 @@ retry:
 			page = target.page;
 			if (isolate_lru_page(page))
 				goto put;
-			pc = lookup_page_cgroup(page);
-			if (!mem_cgroup_move_account(page, 1, pc,
-						     mc.from, mc.to)) {
+			if (!mem_cgroup_move_account(page, 1, mc.from, mc.to)) {
 				mc.precharge--;
 				/* we uncharge from mc.from later. */
 				mc.moved_charge++;
@@ -5619,7 +5576,6 @@ static void __init enable_swap_cgroup(void)
 void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 {
 	struct mem_cgroup *memcg;
-	struct page_cgroup *pc;
 	unsigned short oldid;
 
 	VM_BUG_ON_PAGE(PageLRU(page), page);
@@ -5628,8 +5584,7 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 	if (!do_swap_account)
 		return;
 
-	pc = lookup_page_cgroup(page);
-	memcg = pc->mem_cgroup;
+	memcg = page->mem_cgroup;
 
 	/* Readahead page, never charged */
 	if (!memcg)
@@ -5639,7 +5594,7 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 	VM_BUG_ON_PAGE(oldid, page);
 	mem_cgroup_swap_statistics(memcg, true);
 
-	pc->mem_cgroup = NULL;
+	page->mem_cgroup = NULL;
 
 	if (!mem_cgroup_is_root(memcg))
 		page_counter_uncharge(&memcg->memory, 1);
@@ -5706,7 +5661,6 @@ int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
 		goto out;
 
 	if (PageSwapCache(page)) {
-		struct page_cgroup *pc = lookup_page_cgroup(page);
 		/*
 		 * Every swap fault against a single page tries to charge the
 		 * page, bail as early as possible.  shmem_unuse() encounters
@@ -5714,7 +5668,7 @@ int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
 		 * the page lock, which serializes swap cache removal, which
 		 * in turn serializes uncharging.
 		 */
-		if (pc->mem_cgroup)
+		if (page->mem_cgroup)
 			goto out;
 	}
 
@@ -5867,7 +5821,6 @@ static void uncharge_list(struct list_head *page_list)
 	next = page_list->next;
 	do {
 		unsigned int nr_pages = 1;
-		struct page_cgroup *pc;
 
 		page = list_entry(next, struct page, lru);
 		next = page->lru.next;
@@ -5875,23 +5828,22 @@ static void uncharge_list(struct list_head *page_list)
 		VM_BUG_ON_PAGE(PageLRU(page), page);
 		VM_BUG_ON_PAGE(page_count(page), page);
 
-		pc = lookup_page_cgroup(page);
-		if (!pc->mem_cgroup)
+		if (!page->mem_cgroup)
 			continue;
 
 		/*
 		 * Nobody should be changing or seriously looking at
-		 * pc->mem_cgroup at this point, we have fully
+		 * page->mem_cgroup at this point, we have fully
 		 * exclusive access to the page.
 		 */
 
-		if (memcg != pc->mem_cgroup) {
+		if (memcg != page->mem_cgroup) {
 			if (memcg) {
 				uncharge_batch(memcg, pgpgout, nr_anon, nr_file,
 					       nr_huge, page);
 				pgpgout = nr_anon = nr_file = nr_huge = 0;
 			}
-			memcg = pc->mem_cgroup;
+			memcg = page->mem_cgroup;
 		}
 
 		if (PageTransHuge(page)) {
@@ -5905,7 +5857,7 @@ static void uncharge_list(struct list_head *page_list)
 		else
 			nr_file += nr_pages;
 
-		pc->mem_cgroup = NULL;
+		page->mem_cgroup = NULL;
 
 		pgpgout++;
 	} while (next != page_list);
@@ -5924,14 +5876,11 @@ static void uncharge_list(struct list_head *page_list)
  */
 void mem_cgroup_uncharge(struct page *page)
 {
-	struct page_cgroup *pc;
-
 	if (mem_cgroup_disabled())
 		return;
 
 	/* Don't touch page->lru of any random page, pre-check: */
-	pc = lookup_page_cgroup(page);
-	if (!pc->mem_cgroup)
+	if (!page->mem_cgroup)
 		return;
 
 	INIT_LIST_HEAD(&page->lru);
@@ -5968,7 +5917,6 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage,
 			bool lrucare)
 {
 	struct mem_cgroup *memcg;
-	struct page_cgroup *pc;
 	int isolated;
 
 	VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage);
@@ -5983,8 +5931,7 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage,
 		return;
 
 	/* Page cache replacement: new page already charged? */
-	pc = lookup_page_cgroup(newpage);
-	if (pc->mem_cgroup)
+	if (newpage->mem_cgroup)
 		return;
 
 	/*
@@ -5993,15 +5940,14 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage,
 	 * uncharged page when the PFN walker finds a page that
 	 * reclaim just put back on the LRU but has not released yet.
 	 */
-	pc = lookup_page_cgroup(oldpage);
-	memcg = pc->mem_cgroup;
+	memcg = oldpage->mem_cgroup;
 	if (!memcg)
 		return;
 
 	if (lrucare)
 		lock_page_lru(oldpage, &isolated);
 
-	pc->mem_cgroup = NULL;
+	oldpage->mem_cgroup = NULL;
 
 	if (lrucare)
 		unlock_page_lru(oldpage, isolated);