From: Mel Gorman <mgorman@suse.de>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Linux-MM <linux-mm@kvack.org>,
Linux-Netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
David Miller <davem@davemloft.net>, Neil Brown <neilb@suse.de>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH 01/14] mm: Serialize access to min_free_kbytes
Date: Thu, 7 Jul 2011 10:17:44 +0100 [thread overview]
Message-ID: <20110707091744.GF15285@suse.de> (raw)
In-Reply-To: <20110706164447.d571051a.akpm@linux-foundation.org>
On Wed, Jul 06, 2011 at 04:44:47PM -0700, Andrew Morton wrote:
> On Mon, 20 Jun 2011 14:12:07 +0100
> Mel Gorman <mgorman@suse.de> wrote:
>
> > There is a race between the min_free_kbytes sysctl, memory hotplug
> > and transparent hugepage support enablement. Memory hotplug uses a
> > zonelists_mutex to avoid a race when building zonelists. Reuse it to
> > serialise watermark updates.
>
> This patch appears to be a standalone fix, unrelated to the overall
> patch series?
>
Yes. In the original series this would have been a more serious problem
as min_free_kbytes was potentially adjusted more frequently.
> How does one trigger the race and what happens when it hits, btw?
One could trigger the trace by having multiple processes on different
CPUs write to min_free_kbytes. One could add memory hotplug events
to that for extra fun but it is unnecessary to trigger the race.
The consequences are that the value for min_free_kbytes and the zone
watermarks get out of sync. Whether the zone watermarks will be too
high or too low would depend on the timing. For the most part, the
consequence will simply be that the min free level for some zones will
be wrong. A more serious consequence is that totalreserve_pages could
get out of sync and strict no memory overcommit could fail a mmap when
it should have succeeded for the value of min_free_kbytes or suspend
fail because it did not preallocate enough pages.
It's not exactly earth shattering.
--
Mel Gorman
SUSE Labs
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next prev parent reply other threads:[~2011-07-07 9:17 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-20 13:12 [PATCH 00/14] Swap-over-NBD without deadlocking v5 Mel Gorman
2011-06-20 13:12 ` [PATCH 01/14] mm: Serialize access to min_free_kbytes Mel Gorman
2011-07-06 23:44 ` Andrew Morton
2011-07-07 9:17 ` Mel Gorman [this message]
2011-06-20 13:12 ` [PATCH 02/14] mm: sl[au]b: Add knowledge of PFMEMALLOC reserve pages Mel Gorman
2011-06-20 13:12 ` [PATCH 03/14] mm: Introduce __GFP_MEMALLOC to allow access to emergency reserves Mel Gorman
2011-06-20 13:12 ` [PATCH 04/14] mm: allow PF_MEMALLOC from softirq context Mel Gorman
2011-06-20 13:12 ` [PATCH 05/14] mm: Ignore mempolicies when using ALLOC_NO_WATERMARK Mel Gorman
2011-06-20 13:12 ` [PATCH 06/14] net: Introduce sk_allocation() to allow addition of GFP flags depending on the individual socket Mel Gorman
2011-06-20 13:12 ` [PATCH 07/14] netvm: Allow the use of __GFP_MEMALLOC by specific sockets Mel Gorman
2011-06-20 13:12 ` [PATCH 08/14] netvm: Allow skb allocation to use PFMEMALLOC reserves Mel Gorman
2011-06-20 13:12 ` [PATCH 09/14] netvm: Propagate page->pfmemalloc to skb Mel Gorman
2011-06-20 13:12 ` [PATCH 10/14] netvm: Set PF_MEMALLOC as appropriate during SKB processing Mel Gorman
2011-06-20 13:12 ` [PATCH 11/14] mm: Micro-optimise slab to avoid a function call Mel Gorman
2011-06-20 13:12 ` [PATCH 12/14] nbd: Set SOCK_MEMALLOC for access to PFMEMALLOC reserves Mel Gorman
2011-06-20 13:12 ` [PATCH 13/14] mm: Throttle direct reclaimers if PF_MEMALLOC reserves are low and swap is backed by network storage Mel Gorman
2011-06-20 13:12 ` [PATCH 14/14] mm: Account for the number of times direct reclaimers get throttled Mel Gorman
2011-07-06 23:51 ` [PATCH 00/14] Swap-over-NBD without deadlocking v5 Andrew Morton
2011-07-07 9:47 ` Mel Gorman
2011-07-07 12:58 ` Christoph Hellwig
2011-07-15 14:10 ` Mel Gorman
2011-07-15 15:27 ` Christoph Hellwig
-- strict thread matches above, loose matches on Subject: below --
2011-10-06 12:41 [PATCH 00/14] Swap-over-NBD without deadlocking V7 Mel Gorman
2011-10-06 12:41 ` [PATCH 01/14] mm: Serialize access to min_free_kbytes Mel Gorman
2011-09-09 10:57 [PATCH 00/14] Swap-over-NBD without deadlocking v6 Mel Gorman
2011-09-09 10:57 ` [PATCH 01/14] mm: Serialize access to min_free_kbytes Mel Gorman
2011-06-09 8:02 [PATCH 00/14] Swap-over-NBD without deadlocking v4r3 Mel Gorman
2011-06-09 8:02 ` [PATCH 01/14] mm: Serialize access to min_free_kbytes Mel Gorman
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