Messages in this thread | | | Date | Thu, 23 Oct 2014 10:14:43 -0400 | From | Johannes Weiner <> | Subject | Re: [patch 2/2] mm: memcontrol: fix missed end-writeback page accounting |
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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
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