From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vladimir Davydov Subject: Re: [PATCH 2/2] mm: memcontrol: drop unnecessary lru locking from mem_cgroup_migrate() Date: Sun, 7 Feb 2016 21:41:00 +0300 Message-ID: <20160207184059.GB19151@esperanza> References: <1454616467-8994-1-git-send-email-hannes@cmpxchg.org> <1454616467-8994-2-git-send-email-hannes@cmpxchg.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Return-path: Content-Disposition: inline In-Reply-To: <1454616467-8994-2-git-send-email-hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Transfer-Encoding: 7bit To: Johannes Weiner Cc: Andrew Morton , Hugh Dickins , Michal Hocko , Mateusz Guzik , Sergey Senozhatsky , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kernel-team-b10kYP2dOMg@public.gmane.org On Thu, Feb 04, 2016 at 03:07:47PM -0500, 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 > Suggested-by: Hugh Dickins Acked-by: Vladimir Davydov Nit: diff --git a/mm/memcontrol.c b/mm/memcontrol.c index ae8b81c55685..120118f3ce0a 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5483,6 +5483,7 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage) unsigned int nr_pages; bool compound; + VM_BUG_ON_PAGE(PageLRU(newpage), newpage); VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage); VM_BUG_ON_PAGE(!PageLocked(newpage), newpage); VM_BUG_ON_PAGE(PageAnon(oldpage) != PageAnon(newpage), newpage);