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Commit e94c8a9c authored by KAMEZAWA Hiroyuki's avatar KAMEZAWA Hiroyuki Committed by Linus Torvalds
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memcg: make mem_cgroup_split_huge_fixup() more efficient 



In split_huge_page(), mem_cgroup_split_huge_fixup() is called to handle
page_cgroup modifcations.  It takes move_lock_page_cgroup() and modifies
page_cgroup and LRU accounting jobs and called HPAGE_PMD_SIZE - 1 times.

But thinking again,
  - compound_lock() is held at move_accout...then, it's not necessary
    to take move_lock_page_cgroup().
  - LRU is locked and all tail pages will go into the same LRU as
    head is now on.
  - page_cgroup is contiguous in huge page range.

This patch fixes mem_cgroup_split_huge_fixup() as to be called once per
hugepage and reduce costs for spliting.

[akpm@linux-foundation.org: fix typo, per Michal]
Signed-off-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6b208e3f

include/linux/memcontrol.h

+2 −3
Original line number Diff line number Diff line
@@ -163,7 +163,7 @@ u64 mem_cgroup_get_limit(struct mem_cgroup *memcg); 


void mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx);

#ifdef CONFIG_TRANSPARENT_HUGEPAGE

void mem_cgroup_split_huge_fixup(struct page *head, struct page *tail);

void mem_cgroup_split_huge_fixup(struct page *head);

#endif



#ifdef CONFIG_DEBUG_VM
@@ -379,8 +379,7 @@ u64 mem_cgroup_get_limit(struct mem_cgroup *memcg) 
	return 0;

}



static inline void mem_cgroup_split_huge_fixup(struct page *head,

						struct page *tail)

static inline void mem_cgroup_split_huge_fixup(struct page *head)

{

}

mm/huge_memory.c

+2 −1
Original line number Diff line number Diff line
@@ -1207,6 +1207,8 @@ static void __split_huge_page_refcount(struct page *page) 
	/* prevent PageLRU to go away from under us, and freeze lru stats */

	spin_lock_irq(&zone->lru_lock);

	compound_lock(page);

	/* complete memcg works before add pages to LRU */

	mem_cgroup_split_huge_fixup(page);



	for (i = 1; i < HPAGE_PMD_NR; i++) {

		struct page *page_tail = page + i;
@@ -1278,7 +1280,6 @@ static void __split_huge_page_refcount(struct page *page) 
		BUG_ON(!PageDirty(page_tail));

		BUG_ON(!PageSwapBacked(page_tail));



		mem_cgroup_split_huge_fixup(page, page_tail);



		lru_add_page_tail(zone, page, page_tail);

	}

mm/memcontrol.c

+17 −17
Original line number Diff line number Diff line
@@ -2553,39 +2553,39 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg, 
			(1 << PCG_ACCT_LRU) | (1 << PCG_MIGRATION))

/*

 * Because tail pages are not marked as "used", set it. We're under

 * zone->lru_lock, 'splitting on pmd' and compund_lock.

 * zone->lru_lock, 'splitting on pmd' and compound_lock.

 * charge/uncharge will be never happen and move_account() is done under

 * compound_lock(), so we don't have to take care of races.

 */

void mem_cgroup_split_huge_fixup(struct page *head, struct page *tail)

void mem_cgroup_split_huge_fixup(struct page *head)

{

	struct page_cgroup *head_pc = lookup_page_cgroup(head);

	struct page_cgroup *tail_pc = lookup_page_cgroup(tail);

	unsigned long flags;

	struct page_cgroup *pc;

	int i;



	if (mem_cgroup_disabled())

		return;

	for (i = 1; i < HPAGE_PMD_NR; i++) {

		pc = head_pc + i;

		pc->mem_cgroup = head_pc->mem_cgroup;

		smp_wmb();/* see __commit_charge() */

		/*

	 * We have no races with charge/uncharge but will have races with

	 * page state accounting.

		 * LRU flags cannot be copied because we need to add tail

		 * page to LRU by generic call and our hooks will be called.

		 */

	move_lock_page_cgroup(head_pc, &flags);

		pc->flags = head_pc->flags & ~PCGF_NOCOPY_AT_SPLIT;

	}



	tail_pc->mem_cgroup = head_pc->mem_cgroup;

	smp_wmb(); /* see __commit_charge() */

	if (PageCgroupAcctLRU(head_pc)) {

		enum lru_list lru;

		struct mem_cgroup_per_zone *mz;



		/*

		 * LRU flags cannot be copied because we need to add tail

		 *.page to LRU by generic call and our hook will be called.

		 * We hold lru_lock, then, reduce counter directly.

		 */

		lru = page_lru(head);

		mz = page_cgroup_zoneinfo(head_pc->mem_cgroup, head);

		MEM_CGROUP_ZSTAT(mz, lru) -= 1;

		MEM_CGROUP_ZSTAT(mz, lru) -= HPAGE_PMD_NR - 1;

	}

	tail_pc->flags = head_pc->flags & ~PCGF_NOCOPY_AT_SPLIT;

	move_unlock_page_cgroup(head_pc, &flags);

}

#endif