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memcg: make mem_cgroup_split_huge_fixup() more efficient

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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.

[[email protected]: fix typo, per Michal]
Signed-off-by: KAMEZAWA Hiroyuki <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Reviewed-by: Michal Hocko <[email protected]>
Cc: Balbir Singh <[email protected]>
Cc: David Rientjes <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
KAMEZAWA Hiroyuki 2012-01-12 17:18:20 -08:00 • committed by Linus Torvalds
commit e94c8a9cbc
3 changed files with 21 additions and 21 deletions
Download patch file Download diff file Expand all files Collapse all files

34
mm/memcontrol.c
View file

@ -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;
/*
* We have no races with charge/uncharge but will have races with
* page state accounting.
*/
move_lock_page_cgroup(head_pc, &flags);
for (i = 1; i < HPAGE_PMD_NR; i++) {
pc = head_pc + i;
pc->mem_cgroup = head_pc->mem_cgroup;
smp_wmb();/* see __commit_charge() */
/*
* LRU flags cannot be copied because we need to add tail
* page to LRU by generic call and our hooks will be called.
*/
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