From: Michel Lespinasse <walken@google.com>
To: Mel Gorman <mgorman@suse.de>
Cc: Zhouping Liu <zliu@redhat.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Ingo Molnar <mingo@redhat.com>,
Johannes Weiner <jweiner@redhat.com>,
hughd@google.com, Rik van Riel <riel@redhat.com>,
Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH] mm: thp: Acquire the anon_vma rwsem for lock during split
Date: Fri, 4 Jan 2013 17:32:17 -0800 [thread overview]
Message-ID: <CANN689E8S5mmszQoeaYgL_SYe1piBDTWCk-Gy1kxcg6hPfUPwA@mail.gmail.com> (raw)
In-Reply-To: <20130104140815.GA26005@suse.de>
On Fri, Jan 4, 2013 at 6:08 AM, Mel Gorman <mgorman@suse.de> wrote:
> Despite the reason for these commits, NUMA balancing is not the direct
> source of the problem. split_huge_page() expected the anon_vma lock to be
> exclusive to serialise the whole split operation. Ordinarily it is expected
> that the anon_vma lock would only be required when updating the avcs but
> THP also uses it. The locking requirements for THP are complex and there
> is some overlap but broadly speaking they include the following
>
> 1. mmap_sem for read or write prevents THPs being created underneath
> 2. anon_vma is taken for write if collapsing a huge page
> 3. mm->page_table_lock should be taken when checking if pmd_trans_huge as
> split_huge_page can run in parallel
> 4. wait_split_huge_page uses anon_vma taken for write mode to serialise
> against other THP operations
> 5. compound_lock is used to serialise between
> __split_huge_page_refcount() and gup
>
> split_huge_page takes anon_vma for read but that does not serialise against
> parallel split_huge_page operations on the same page (rule 2). One process
> could be modifying the ref counts while the other modifies the page tables
> leading to counters not being reliable. This patch takes the anon_vma
> lock for write to serialise against parallel split_huge_page and parallel
> collapse operations as it is the most fine-grained lock available that
> protects against both.
Your comment about this being the most fine-grained lock made me
think, couldn't we use lock_page() on the THP page here ?
Now I don't necessarily want to push you that direction, because I
haven't fully thought it trough and because what you propose brings us
closer to what happened before anon_vma became an rwlock, which is
more obviously safe. But I felt I should still mention it, since we're
really only trying to protect from concurrent operations on the same
THP page, so locking at just that granularity would seem desirable.
--
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
next prev parent reply other threads:[~2013-01-05 1:32 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1621091901.34838094.1356409676820.JavaMail.root@redhat.com>
2012-12-25 4:38 ` kernel BUG at mm/huge_memory.c:1798! Zhouping Liu
2012-12-25 12:05 ` Hillf Danton
2012-12-26 2:55 ` Zhouping Liu
2012-12-27 0:31 ` Alexander Beregalov
2012-12-27 12:12 ` Hillf Danton
2012-12-27 16:08 ` Alex Xu
2012-12-29 7:22 ` Hillf Danton
2012-12-26 11:22 ` BUG: unable to handle kernel NULL pointer dereference at 0000000000000500 Zhouping Liu
2012-12-26 12:01 ` Hillf Danton
2012-12-26 13:24 ` Zhouping Liu
2012-12-26 15:14 ` Hillf Danton
2012-12-26 14:59 ` Zlatko Calusic
2012-12-27 14:58 ` Zlatko Calusic
2012-12-27 23:55 ` David R. Piegdon
2012-12-28 0:09 ` Zlatko Calusic
2012-12-28 2:45 ` Zhouping Liu
2012-12-28 2:48 ` Zhouping Liu
2012-12-28 9:01 ` Zhouping Liu
2012-12-28 13:43 ` Zlatko Calusic
2012-12-28 12:57 ` Zlatko Calusic
2013-01-03 17:57 ` kernel BUG at mm/huge_memory.c:1798! Mel Gorman
2013-01-04 14:08 ` [PATCH] mm: thp: Acquire the anon_vma rwsem for lock during split Mel Gorman
2013-01-04 21:28 ` Hugh Dickins
2013-01-07 14:36 ` Mel Gorman
2013-01-07 14:39 ` [PATCH] mm: thp: Acquire the anon_vma rwsem for write " Mel Gorman
2013-01-05 1:32 ` Michel Lespinasse [this message]
2013-01-05 12:24 ` [PATCH] mm: thp: Acquire the anon_vma rwsem for lock " Simon Jeons
2013-01-07 15:09 ` Mel Gorman
2013-01-07 15:08 ` Mel Gorman
2013-01-05 5:51 ` Zhouping Liu
2013-01-07 14:38 ` Mel Gorman
2013-01-05 12:21 ` Simon Jeons
2013-01-04 16:58 ` kernel BUG at mm/huge_memory.c:1798! Zhouping Liu
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