From: Andi Kleen <andi@firstfloor.org>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Michel Lespinasse <walken@google.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm: munlock use mapcount to avoid terrible overhead
Date: Tue, 18 Oct 2011 17:25:48 -0700 [thread overview]
Message-ID: <m262jlzv1v.fsf@firstfloor.org> (raw)
In-Reply-To: <alpine.LSU.2.00.1110181700400.3361@sister.anvils> (Hugh Dickins's message of "Tue, 18 Oct 2011 17:02:56 -0700 (PDT)")
Hugh Dickins <hughd@google.com> writes:
> A process spent 30 minutes exiting, just munlocking the pages of a large
> anonymous area that had been alternately mprotected into page-sized vmas:
> for every single page there's an anon_vma walk through all the other
> little vmas to find the right one.
We had the same problem recently after a mmap+touch workload: in this
case it was hugepaged walking all these anon_vmas and the list was over
100k long.
Had some data on this at plumbers:
http://halobates.de/plumbers-fork-locks_v2.pdf
> A general fix to that would be a lot more complicated (use prio_tree on
> anon_vma?), but there's one very simple thing we can do to speed up the
> common case: if a page to be munlocked is mapped only once, then it is
> our vma that it is mapped into, and there's no need whatever to walk
> through all the others.
I think we need a generic fix, this problem does not only happen
in munmap.
-Andi
--
ak@linux.intel.com -- Speaking for myself only
WARNING: multiple messages have this Message-ID (diff)
From: Andi Kleen <andi@firstfloor.org>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Michel Lespinasse <walken@google.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm: munlock use mapcount to avoid terrible overhead
Date: Tue, 18 Oct 2011 17:25:48 -0700 [thread overview]
Message-ID: <m262jlzv1v.fsf@firstfloor.org> (raw)
In-Reply-To: <alpine.LSU.2.00.1110181700400.3361@sister.anvils> (Hugh Dickins's message of "Tue, 18 Oct 2011 17:02:56 -0700 (PDT)")
Hugh Dickins <hughd@google.com> writes:
> A process spent 30 minutes exiting, just munlocking the pages of a large
> anonymous area that had been alternately mprotected into page-sized vmas:
> for every single page there's an anon_vma walk through all the other
> little vmas to find the right one.
We had the same problem recently after a mmap+touch workload: in this
case it was hugepaged walking all these anon_vmas and the list was over
100k long.
Had some data on this at plumbers:
http://halobates.de/plumbers-fork-locks_v2.pdf
> A general fix to that would be a lot more complicated (use prio_tree on
> anon_vma?), but there's one very simple thing we can do to speed up the
> common case: if a page to be munlocked is mapped only once, then it is
> our vma that it is mapped into, and there's no need whatever to walk
> through all the others.
I think we need a generic fix, this problem does not only happen
in munmap.
-Andi
--
ak@linux.intel.com -- Speaking for myself only
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next prev parent reply other threads:[~2011-10-19 0:25 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-19 0:02 [PATCH] mm: munlock use mapcount to avoid terrible overhead Hugh Dickins
2011-10-19 0:02 ` Hugh Dickins
2011-10-19 0:14 ` Andrew Morton
2011-10-19 0:14 ` Andrew Morton
2011-10-19 0:56 ` Hugh Dickins
2011-10-19 0:56 ` Hugh Dickins
2011-10-19 0:25 ` Andi Kleen [this message]
2011-10-19 0:25 ` Andi Kleen
2011-10-19 0:59 ` Hugh Dickins
2011-10-19 0:59 ` Hugh Dickins
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