From: David Miller <davem@davemloft.net>
To: mgorman@suse.de
Cc: akpm@linux-foundation.org, linux-mm@kvack.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
neilb@suse.de, a.p.zijlstra@chello.nl, michaelc@cs.wisc.edu,
emunson@mgebm.net
Subject: Re: [PATCH 05/17] mm: allow PF_MEMALLOC from softirq context
Date: Fri, 11 May 2012 00:39:51 -0400 (EDT) [thread overview]
Message-ID: <20120511.003951.1470088131186301605.davem@davemloft.net> (raw)
In-Reply-To: <1336657510-24378-6-git-send-email-mgorman@suse.de>
From: Mel Gorman <mgorman@suse.de>
Date: Thu, 10 May 2012 14:44:58 +0100
> This is needed to allow network softirq packet processing to make
> use of PF_MEMALLOC.
>
> Currently softirq context cannot use PF_MEMALLOC due to it not being
> associated with a task, and therefore not having task flags to fiddle
> with - thus the gfp to alloc flag mapping ignores the task flags when
> in interrupts (hard or soft) context.
>
> Allowing softirqs to make use of PF_MEMALLOC therefore requires some
> trickery. We basically borrow the task flags from whatever process
> happens to be preempted by the softirq.
>
> So we modify the gfp to alloc flags mapping to not exclude task flags
> in softirq context, and modify the softirq code to save, clear and
> restore the PF_MEMALLOC flag.
>
> The save and clear, ensures the preempted task's PF_MEMALLOC flag
> doesn't leak into the softirq. The restore ensures a softirq's
> PF_MEMALLOC flag cannot leak back into the preempted process.
>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Signed-off-by: Mel Gorman <mgorman@suse.de>
We're now making changes to task->flags from both base and
softirq context, but with non-atomic operations and no other
kind of synchronization.
As far as I can tell, this has to be racy.
If this works via some magic combination of invariants, you
absolutely have to document this, verbosely.
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next prev parent reply other threads:[~2012-05-11 4:40 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-10 13:44 [PATCH 00/17] Swap-over-NBD without deadlocking V10 Mel Gorman
2012-05-10 13:44 ` [PATCH 01/17] mm: Serialize access to min_free_kbytes Mel Gorman
2012-05-10 13:44 ` [PATCH 02/17] mm: sl[au]b: Add knowledge of PFMEMALLOC reserve pages Mel Gorman
2012-05-10 13:44 ` [PATCH 03/17] mm: slub: Optimise the SLUB fast path to avoid pfmemalloc checks Mel Gorman
2012-05-10 13:44 ` [PATCH 04/17] mm: Introduce __GFP_MEMALLOC to allow access to emergency reserves Mel Gorman
2012-05-10 13:44 ` [PATCH 05/17] mm: allow PF_MEMALLOC from softirq context Mel Gorman
2012-05-11 4:39 ` David Miller [this message]
2012-05-14 10:02 ` Mel Gorman
2012-05-15 13:07 ` Mel Gorman
2012-05-10 13:44 ` [PATCH 06/17] mm: Only set page->pfmemalloc when ALLOC_NO_WATERMARKS was used Mel Gorman
2012-05-10 13:45 ` [PATCH 07/17] mm: Ignore mempolicies when using ALLOC_NO_WATERMARK Mel Gorman
2012-05-10 13:45 ` [PATCH 08/17] net: Introduce sk_allocation() to allow addition of GFP flags depending on the individual socket Mel Gorman
2012-05-11 4:49 ` David Miller
2012-05-11 14:12 ` Mel Gorman
2012-05-10 13:45 ` [PATCH 09/17] netvm: Allow the use of __GFP_MEMALLOC by specific sockets Mel Gorman
2012-05-11 4:50 ` David Miller
2012-05-10 13:45 ` [PATCH 10/17] netvm: Allow skb allocation to use PFMEMALLOC reserves Mel Gorman
2012-05-11 4:57 ` David Miller
2012-05-11 14:32 ` Mel Gorman
2012-05-11 14:42 ` Peter Zijlstra
2012-05-11 15:07 ` Mel Gorman
2012-05-11 21:17 ` David Miller
2012-05-10 13:45 ` [PATCH 11/17] netvm: Propagate page->pfmemalloc to skb Mel Gorman
2012-05-10 13:45 ` [PATCH 12/17] netvm: Propagate page->pfmemalloc from netdev_alloc_page " Mel Gorman
2012-05-11 5:01 ` David Miller
2012-05-11 14:46 ` Mel Gorman
2012-05-10 13:45 ` [PATCH 13/17] netvm: Set PF_MEMALLOC as appropriate during SKB processing Mel Gorman
2012-05-11 5:03 ` David Miller
2012-05-10 13:45 ` [PATCH 14/17] mm: Micro-optimise slab to avoid a function call Mel Gorman
2012-05-10 13:45 ` [PATCH 15/17] nbd: Set SOCK_MEMALLOC for access to PFMEMALLOC reserves Mel Gorman
2012-05-10 13:45 ` [PATCH 16/17] mm: Throttle direct reclaimers if PF_MEMALLOC reserves are low and swap is backed by network storage Mel Gorman
2012-05-10 13:45 ` [PATCH 17/17] mm: Account for the number of times direct reclaimers get throttled Mel Gorman
2012-05-10 17:17 ` [PATCH 00/17] Swap-over-NBD without deadlocking V10 Mike Christie
2012-05-11 5:04 ` David Miller
2012-05-11 15:45 ` Mel Gorman
2012-05-11 21:23 ` David Miller
2012-05-11 21:29 ` Andrew Morton
2012-05-14 11:10 ` Mel Gorman
-- strict thread matches above, loose matches on Subject: below --
2012-05-17 14:50 [PATCH 00/17] Swap-over-NBD without deadlocking V11 Mel Gorman
2012-05-17 14:50 ` [PATCH 05/17] mm: allow PF_MEMALLOC from softirq context Mel Gorman
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