From: Michal Hocko <mhocko@kernel.org>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
linux-arch@vger.kernel.org
Subject: Re: [PATCH 04/20] arm: get rid of superfluous __GFP_REPEAT
Date: Fri, 29 Apr 2016 11:41:52 +0200 [thread overview]
Message-ID: <20160429094152.GF21977@dhcp22.suse.cz> (raw)
In-Reply-To: <20160428150831.GK31489@dhcp22.suse.cz>
On Thu 28-04-16 17:08:31, Michal Hocko wrote:
> On Thu 28-04-16 15:55:45, Russell King - ARM Linux wrote:
> > On Thu, Apr 28, 2016 at 03:23:50PM +0200, Michal Hocko wrote:
> > > From: Michal Hocko <mhocko@suse.com>
> > >
> > > __GFP_REPEAT has a rather weak semantic but since it has been introduced
> > > around 2.6.12 it has been ignored for low order allocations.
> > >
> > > PGALLOC_GFP uses __GFP_REPEAT but none of the allocation which uses
> > > this flag is for more than order-2. This means that this flag has never
> > > been actually useful here because it has always been used only for
> > > PAGE_ALLOC_COSTLY requests.
> >
> > I'm unconvinced. Back in 2013, I was seeing a lot of failures, so:
> >
> > commit 8c65da6dc89ccb605d73773b1dd617e72982d971
> > Author: Russell King <rmk+kernel@arm.linux.org.uk>
> > Date: Sat Nov 30 12:52:31 2013 +0000
> >
> > ARM: pgd allocation: retry on failure
> >
> > Make pgd allocation retry on failure; we really need this to succeed
> > otherwise fork() can trigger OOMs.
> >
> > Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
> >
> > Maybe something has changed again in the MM layer which makes this flag
> > unnecessary again, and it was a temporary blip around that time, I don't
> > know.
>
> PAGE_ALLOC_COSTLY_ORDER is defined to order 3 since 2007 and even before
> the code was doing
> - if ((order <= 3) || (gfp_mask & __GFP_REPEAT))
> + if ((order <= PAGE_ALLOC_COSTLY_ORDER) ||
> + (gfp_mask & __GFP_REPEAT))
> do_retry = 1;
>
> So an order-2 allocation which is the case for this particular code now
> will trigger the OOM killer and fail only when the current task is
> killed by the OOM killer. Other than that order-2 is basically
> GFP_NOFAIL. Have a look at __alloc_pages_slowpath() for more details.
Does this explanation help?
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2016-04-29 9:41 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-28 13:23 [PATCH 0/19] get rid of superfluous __GFP_REPEAT Michal Hocko
2016-04-28 13:23 ` [PATCH 01/20] tree wide: get rid of __GFP_REPEAT for order-0 allocations part I Michal Hocko
2016-04-28 13:23 ` [PATCH 02/20] x86: get rid of superfluous __GFP_REPEAT Michal Hocko
2016-04-28 13:23 ` [PATCH 03/20] x86/efi: " Michal Hocko
2016-04-28 13:23 ` [PATCH 04/20] arm: " Michal Hocko
2016-04-28 14:55 ` Russell King - ARM Linux
2016-04-28 15:08 ` Michal Hocko
2016-04-29 9:41 ` Michal Hocko [this message]
2016-04-28 13:23 ` [PATCH 05/20] arm64: " Michal Hocko
2016-04-28 13:23 ` [PATCH 06/20] arc: " Michal Hocko
2016-04-28 13:23 ` [PATCH 07/20] mips: " Michal Hocko
2016-04-28 13:23 ` [PATCH 08/20] nios2: " Michal Hocko
2016-04-28 13:23 ` [PATCH 09/20] parisc: " Michal Hocko
2016-04-28 13:23 ` [PATCH 10/20] score: " Michal Hocko
2016-04-28 13:23 ` [PATCH 11/20] powerpc: " Michal Hocko
2016-04-28 13:23 ` [PATCH 12/20] sparc: " Michal Hocko
2016-04-28 13:23 ` [PATCH 13/20] s390: " Michal Hocko
2016-04-28 13:24 ` [PATCH 14/20] sh: " Michal Hocko
2016-04-28 13:24 ` [PATCH 15/20] tile: " Michal Hocko
2016-04-28 16:21 ` Chris Metcalf
2016-04-28 13:24 ` [PATCH 16/20] unicore32: " Michal Hocko
2016-04-28 13:24 ` [PATCH 17/20] dm: get rid of superfluous gfp flags Michal Hocko
2016-04-29 18:54 ` Mike Snitzer
2016-05-02 7:31 ` Michal Hocko
2016-04-28 13:24 ` [PATCH 18/20] dm: clean up GFP_NIO usage Michal Hocko
2016-04-28 14:20 ` Mikulas Patocka
2016-04-28 14:41 ` Michal Hocko
2016-04-28 13:24 ` [PATCH 19/20] md: simplify free_params for kmalloc vs vmalloc fallback Michal Hocko
2016-04-28 14:51 ` [PATCH] " Michal Hocko
2016-04-28 15:04 ` Mikulas Patocka
2016-04-28 15:28 ` Michal Hocko
2016-04-28 15:40 ` Mikulas Patocka
2016-04-28 16:59 ` Michal Hocko
2016-04-28 15:37 ` [PATCH 19/20] " Mike Snitzer
2016-04-28 16:00 ` Michal Hocko
2016-04-28 13:24 ` [PATCH 20/20] jbd2: get rid of superfluous __GFP_REPEAT Michal Hocko
2016-05-12 16:53 ` [PATCH 0/19] " Michal Hocko
2016-05-12 20:13 ` Andrew Morton
2016-05-13 6:58 ` Michal Hocko
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