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Date: Thu, 23 Oct 2014 10:14:43 -0400 From: Johannes Weiner <hannes@...xchg.org> To: Michal Hocko <mhocko@...e.cz> Cc: Andrew Morton <akpm@...ux-foundation.org>, Vladimir Davydov <vdavydov@...allels.com>, linux-mm@...ck.org, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [patch 2/2] mm: memcontrol: fix missed end-writeback page accounting On Thu, Oct 23, 2014 at 03:03:31PM +0200, Michal Hocko wrote: > On Wed 22-10-14 14:29:28, Johannes Weiner wrote: > > 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API") changed page > > migration to uncharge the old page right away. The page is locked, > > unmapped, truncated, and off the LRU, but it could race with writeback > > ending, which then doesn't unaccount the page properly: > > > > test_clear_page_writeback() migration > > acquire pc->mem_cgroup->move_lock > > I do not think that mentioning move_lock is important/helpful here > because the hot path which is taken all the time (except when there is a > task move in progress) doesn't take it. > Besides that it is not even relevant for the race. You're right. It's not worth mentioning the transaction setup/finish at all, because migration does not participate in that protocol. How about this? Andrew, could you please copy-paste this into the patch? test_clear_page_writeback() migration wait_on_page_writeback() TestClearPageWriteback() mem_cgroup_migrate() clear PCG_USED mem_cgroup_update_page_stat() if (PageCgroupUsed(pc)) decrease memcg pages under writeback -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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