Messages in this thread Patch in this message | | | Date | Fri, 23 May 2014 15:39:38 +0200 | From | Michal Hocko <> | Subject | Re: [patch 7/9] mm: memcontrol: do not acquire page_cgroup lock for kmem pages |
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I am adding Vladimir to CC
On Wed 30-04-14 16:25:41, Johannes Weiner wrote: > Kmem page charging and uncharging is serialized by means of exclusive > access to the page. Do not take the page_cgroup lock and don't set > pc->flags atomically. > > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
The patch is correct I just have some comments below. Anyway Acked-by: Michal Hocko <mhocko@suse.cz>
> --- > mm/memcontrol.c | 16 +++------------- > 1 file changed, 3 insertions(+), 13 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index c528ae9ac230..d3961fce1d54 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3535,10 +3535,8 @@ void __memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg, > } >
/* * given page is newly allocated and invisible to everybody but * the caller so there is no need to use page_cgroup lock nor * SetPageCgroupUsed */
would be helpful?
> pc = lookup_page_cgroup(page); > - lock_page_cgroup(pc); > pc->mem_cgroup = memcg; > - SetPageCgroupUsed(pc); > - unlock_page_cgroup(pc); > + pc->flags = PCG_USED; > } > > void __memcg_kmem_uncharge_pages(struct page *page, int order) > @@ -3548,19 +3546,11 @@ void __memcg_kmem_uncharge_pages(struct page *page, int order) > > > pc = lookup_page_cgroup(page); > - /* > - * Fast unlocked return. Theoretically might have changed, have to > - * check again after locking. > - */
This comment was there since the code has been merged. Maybe it was true at the time but after "mm: get rid of __GFP_KMEMCG" it is definitely out of date.
/* * the pages is going away and will be freed and nobody can see * it anymore so no need to take page_cgroup lock. */ > if (!PageCgroupUsed(pc)) > return; > > - lock_page_cgroup(pc); > - if (PageCgroupUsed(pc)) { > - memcg = pc->mem_cgroup; > - ClearPageCgroupUsed(pc); > - } > - unlock_page_cgroup(pc);
maybe add WARN_ON_ONCE(pc->flags != PCG_USED);
to check for an unexpected flags usage in the kmem path?
> + memcg = pc->mem_cgroup; > + pc->flags = 0; > > /* > * We trust that only if there is a memcg associated with the page, it > -- > 1.9.2 >
-- Michal Hocko SUSE Labs
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