From: Mel Gorman <mgorman@suse.de>
To: NeilBrown <neilb@suse.de>
Cc: Linux-MM <linux-mm@kvack.org>,
Linux-Netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH 12/12] mm: Throttle direct reclaimers if PF_MEMALLOC reserves are low and swap is backed by network storage
Date: Mon, 18 Apr 2011 15:08:04 +0100 [thread overview]
Message-ID: <20110418140804.GC16908@suse.de> (raw)
In-Reply-To: <20110418223251.7ab148bb@notabene.brown>
On Mon, Apr 18, 2011 at 10:32:51PM +1000, NeilBrown wrote:
> On Thu, 14 Apr 2011 11:41:38 +0100 Mel Gorman <mgorman@suse.de> wrote:
>
> > If swap is backed by network storage such as NBD, there is a risk that a
> > large number of reclaimers can hang the system by consuming all
> > PF_MEMALLOC reserves. To avoid these hangs, the administrator must tune
> > min_free_kbytes in advance. This patch will throttle direct reclaimers
> > if half the PF_MEMALLOC reserves are in use as the system is at risk of
> > hanging. A message will be displayed so the administrator knows that
> > min_free_kbytes should be tuned to a higher value to avoid the
> > throttling in the future.
> >
>
> (I knew there was something else).
>
> I understand that there are suggestions that direct reclaim should always be
> serialised as this reduces lock contention and improve data patterns (or
> something like that).
>
AFAIK, this suggestion never got much beyond the "hand-waving" stage
of development. It tended to trip up on the fact that such a feature
could also throttle processes on machines with plenty of free clean
unmapped pagecache which would be undesirable.
> Would that make this patch redundant?
Depends on how it was being serialised but ....
> Or does this provide some extra
> guarantee that the other proposal would not?
>
This patch could be extended to serialise direct reclaims in situations
other than PFMEMALLOC is low if someone demonstrated the benefit.
--
Mel Gorman
SUSE Labs
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prev parent reply other threads:[~2011-04-18 14:08 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-14 10:41 [PATCH 00/12] Swap-over-NBD without deadlocking v1 Mel Gorman
2011-04-14 10:41 ` [PATCH 01/12] mm: Serialize access to min_free_kbytes Mel Gorman
2011-04-14 10:41 ` [PATCH 02/12] mm: sl[au]b: Add knowledge of PFMEMALLOC reserve pages Mel Gorman
2011-04-14 10:41 ` [PATCH 03/12] mm: Introduce __GFP_MEMALLOC to allow access to emergency reserves Mel Gorman
2011-04-14 10:41 ` [PATCH 04/12] mm: allow PF_MEMALLOC from softirq context Mel Gorman
2011-04-14 10:41 ` [PATCH 05/12] mm: Ignore mempolicies when using ALLOC_NO_WATERMARK Mel Gorman
2011-04-14 10:41 ` [PATCH 06/12] net: Introduce sk_allocation() to allow addition of GFP flags depending on the individual socket Mel Gorman
2011-04-14 10:41 ` [PATCH 07/12] netvm: Allow the use of __GFP_MEMALLOC by specific sockets Mel Gorman
2011-04-14 10:41 ` [PATCH 08/12] netvm: Allow skb allocation to use PFMEMALLOC reserves Mel Gorman
2011-04-14 21:33 ` David Miller
2011-04-15 10:44 ` Mel Gorman
2011-04-14 10:41 ` [PATCH 09/12] netvm: Set PF_MEMALLOC as appropriate during SKB processing Mel Gorman
2011-04-14 10:41 ` [PATCH 10/12] mm: Micro-optimise slab to avoid a function call Mel Gorman
2011-04-14 10:41 ` [PATCH 11/12] nbd: Set SOCK_MEMALLOC for access to PFMEMALLOC reserves Mel Gorman
2011-04-14 10:41 ` [PATCH 12/12] mm: Throttle direct reclaimers if PF_MEMALLOC reserves are low and swap is backed by network storage Mel Gorman
2011-04-18 12:30 ` NeilBrown
2011-04-18 14:04 ` Mel Gorman
2011-04-18 12:32 ` NeilBrown
2011-04-18 14:08 ` Mel Gorman [this message]
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