linux-kernel - Re: [PATCH for 3.2.34] memcg: do not trigger OOM from add_to_page_cache

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Date:	Thu, 06 Dec 2012 11:12:49 +0100
From:	"azurIt" <azurit@...ox.sk>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
	cgroups mailinglist <cgroups@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH for 3.2.34] memcg: do not trigger OOM from add_to_page_cache_locked

>Dohh. The very same stack mem_cgroup_newpage_charge called from the page
>fault. The heavy inlining is not particularly helping here... So there
>must be some other THP charge leaking out.
>[/me is diving into the code again]
>
>* do_huge_pmd_anonymous_page falls back to handle_pte_fault
>* do_huge_pmd_wp_page_fallback falls back to simple pages so it doesn't
>  charge the huge page
>* do_huge_pmd_wp_page splits the huge page and retries with fallback to
>  handle_pte_fault
>* collapse_huge_page is not called in the page fault path
>* do_wp_page, do_anonymous_page and __do_fault  operate on a single page
>  so the memcg charging cannot return ENOMEM
>
>There are no other callers AFAICS so I am getting clueless. Maybe more
>debugging will tell us something (the inlining has been reduced for thp
>paths which can reduce performance in thp page fault heavy workloads but
>this will give us better traces - I hope).


Should i apply all patches togather? (fix for this bug, more log messages, backported fix from 3.5 and this new one)


>Anyway do you see the same problem if transparent huge pages are
>disabled?
>echo never > /sys/kernel/mm/transparent_hugepage/enabled)


# cat /sys/kernel/mm/transparent_hugepage/enabled
cat: /sys/kernel/mm/transparent_hugepage/enabled: No such file or directory
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