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From: Rik van Riel <riel@redhat.com>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Mel Gorman <mel@csn.ul.ie>,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
	"Jun'ichi Nomura" <j-nomura@ce.jp.nec.com>,
	Andi Kleen <ak@linux.intel.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: fix migration hangs on anon_vma lock
Date: Tue, 11 Jan 2011 15:35:12 -0500	[thread overview]
Message-ID: <4D2CBF00.1080706@redhat.com> (raw)
In-Reply-To: <alpine.LSU.2.00.1101102259160.24988@sister.anvils>

On 01/11/2011 02:08 AM, Hugh Dickins wrote:
> Increased usage of page migration in mmotm reveals that the anon_vma
> locking in unmap_and_move() has been deficient since 2.6.36 (or even
> earlier).  Review at the time of f18194275c39835cb84563500995e0d503a32d9a
> "mm: fix hang on anon_vma->root->lock" missed the issue here: the anon_vma
> to which we get a reference may already have been freed back to its slab
> (it is in use when we check page_mapped, but that can change), and so its
> anon_vma->root may be switched at any moment by reuse in anon_vma_prepare.
>
> Perhaps we could fix that with a get_anon_vma_unless_zero(), but let's not:
> just rely on page_lock_anon_vma() to do all the hard thinking for us, then
> we don't need any rcu read locking over here.
>
> In removing the rcu_unlock label: since PageAnon is a bit in page->mapping,
> it's impossible for a !page->mapping page to be anon; but insert VM_BUG_ON
> in case the implementation ever changes.
>
> Signed-off-by: Hugh Dickins<hughd@google.com>
> Cc: stable@kernel.org [2.6.37, 2.6.36]

Reviewed-by: Rik van Riel <riel@redhat.com>

-- 
All rights reversed

WARNING: multiple messages have this Message-ID (diff)
From: Rik van Riel <riel@redhat.com>
To: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Mel Gorman <mel@csn.ul.ie>,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
	Jun'ichi Nomura <j-nomura@ce.jp.nec.com>,
	Andi Kleen <ak@linux.intel.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: fix migration hangs on anon_vma lock
Date: Tue, 11 Jan 2011 15:35:12 -0500	[thread overview]
Message-ID: <4D2CBF00.1080706@redhat.com> (raw)
In-Reply-To: <alpine.LSU.2.00.1101102259160.24988@sister.anvils>

On 01/11/2011 02:08 AM, Hugh Dickins wrote:
> Increased usage of page migration in mmotm reveals that the anon_vma
> locking in unmap_and_move() has been deficient since 2.6.36 (or even
> earlier).  Review at the time of f18194275c39835cb84563500995e0d503a32d9a
> "mm: fix hang on anon_vma->root->lock" missed the issue here: the anon_vma
> to which we get a reference may already have been freed back to its slab
> (it is in use when we check page_mapped, but that can change), and so its
> anon_vma->root may be switched at any moment by reuse in anon_vma_prepare.
>
> Perhaps we could fix that with a get_anon_vma_unless_zero(), but let's not:
> just rely on page_lock_anon_vma() to do all the hard thinking for us, then
> we don't need any rcu read locking over here.
>
> In removing the rcu_unlock label: since PageAnon is a bit in page->mapping,
> it's impossible for a !page->mapping page to be anon; but insert VM_BUG_ON
> in case the implementation ever changes.
>
> Signed-off-by: Hugh Dickins<hughd@google.com>
> Cc: stable@kernel.org [2.6.37, 2.6.36]

Reviewed-by: Rik van Riel <riel@redhat.com>

-- 
All rights reversed

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  parent reply	other threads:[~2011-01-11 20:36 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-11  7:08 [PATCH] mm: fix migration hangs on anon_vma lock Hugh Dickins
2011-01-11  7:08 ` Hugh Dickins
2011-01-11  7:10 ` [PATCH] mm: fix hugepage migration in the same way Hugh Dickins
2011-01-11  7:10   ` Hugh Dickins
2011-01-11 11:44 ` [PATCH] mm: fix migration hangs on anon_vma lock Mel Gorman
2011-01-11 11:44   ` Mel Gorman
2011-01-11 20:35 ` Rik van Riel [this message]
2011-01-11 20:35   ` Rik van Riel

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