From: Mel Gorman <mgorman@suse.de>
To: David Miller <davem@davemloft.net>
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: Tue, 15 May 2012 14:07:48 +0100 [thread overview]
Message-ID: <20120515130748.GI29102@suse.de> (raw)
In-Reply-To: <20120514100229.GA29102@suse.de>
On Mon, May 14, 2012 at 11:02:29AM +0100, Mel Gorman wrote:
> Softirqs can run on multiple CPUs sure but the same task should not be
> executing the same softirq code. Interrupts are disabled and the
> executing process cannot sleep in softirq context so the task flags
> cannot "leak" nor can they be concurrently modified.
>
This comment about hardirq is obviously wrong as __do_softirq() enables
interrupts and can be preempted by a hardirq. I've updated the changelog
now to include the following;
Softirqs can run on multiple CPUs sure but the same task should not be
executing the same softirq code. Neither should the softirq
handler be preempted by any other softirq handler so the flags
should not leak to an unrelated softirq.
Softirqs re-enable hardware interrupts in __do_softirq() so can be
preempted by hardware interrupts so PF_MEMALLOC is inherited
by the hard IRQ. However, this is similar to a process in
reclaim being preempted by a hardirq. While PF_MEMALLOC is
set, gfp_to_alloc_flags() distinguishes between hard and
soft irqs and avoids giving a hardirq the ALLOC_NO_WATERMARKS
flag.
If the softirq is deferred to ksoftirq then its flags may be used
instead of a normal tasks but as the softirq cannot be preempted,
the PF_MEMALLOC flag does not leak to other code by accident.
--
Mel Gorman
SUSE Labs
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next prev parent reply other threads:[~2012-05-15 13:07 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
2012-05-14 10:02 ` Mel Gorman
2012-05-15 13:07 ` Mel Gorman [this message]
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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