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Date: Fri, 4 Mar 2016 19:04:11 +0100 From: Michal Hocko <mhocko@...nel.org> To: Johannes Weiner <hannes@...xchg.org> Cc: Andrew Morton <akpm@...ux-foundation.org>, Hugh Dickins <hughd@...gle.com>, Vladimir Davydov <vdavydov@...tuozzo.com>, Mateusz Guzik <mguzik@...hat.com>, Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>, linux-mm@...ck.org, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org, kernel-team@...com Subject: Re: [PATCH 2/2] mm: memcontrol: drop unnecessary lru locking from mem_cgroup_migrate() On Thu 04-02-16 15:07:47, Johannes Weiner wrote: > Migration accounting in the memory controller used to have to handle > both oldpage and newpage being on the LRU already; fuse's page cache > replacement used to pass a recycled newpage that had been uncharged > but not freed and removed from the LRU, and the memcg migration code > used to uncharge oldpage to "pass on" the existing charge to newpage. > > Nowadays, pages are no longer uncharged when truncated from the page > cache, but rather only at free time, so if a LRU page is recycled in > page cache replacement it'll also still be charged. And we bail out of > the charge transfer altogether in that case. Tell commit_charge() that > we know newpage is not on the LRU, to avoid taking the zone->lru_lock > unnecessarily from the migration path. > > But also, oldpage is no longer uncharged inside migration. We only use > oldpage for its page->mem_cgroup and page size, so we don't care about > its LRU state anymore either. Remove any mention from the kernel doc. > > Signed-off-by: Johannes Weiner <hannes@...xchg.org> > Suggested-by: Hugh Dickins <hughd@...gle.com> Acked-by: Michal Hocko <mhocko@...e.com> > --- > mm/memcontrol.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 3e4199830456..42882c1e7fce 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -5489,7 +5489,6 @@ void mem_cgroup_uncharge_list(struct list_head *page_list) > * be uncharged upon free. > * > * Both pages must be locked, @newpage->mapping must be set up. > - * Either or both pages might be on the LRU already. > */ > void mem_cgroup_migrate(struct page *oldpage, struct page *newpage) > { > @@ -5524,7 +5523,7 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage) > page_counter_charge(&memcg->memsw, nr_pages); > css_get_many(&memcg->css, nr_pages); > > - commit_charge(newpage, memcg, true); > + commit_charge(newpage, memcg, false); > > local_irq_disable(); > mem_cgroup_charge_statistics(memcg, newpage, compound, nr_pages); > -- > 2.7.0 -- Michal Hocko SUSE Labs
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