From: Johannes Weiner <hannes@cmpxchg.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>,
Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
Mel Gorman <mgorman@suse.de>,
David Rientjes <rientjes@google.com>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH] mm: consolidate GFP_NOFAIL checks in the allocator slowpath
Date: Wed, 14 Dec 2016 15:35:30 -0500 [thread overview]
Message-ID: <20161214203530.GA18561@cmpxchg.org> (raw)
In-Reply-To: <20161214150706.27412-1-mhocko@kernel.org>
On Wed, Dec 14, 2016 at 04:07:06PM +0100, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
>
> Tetsuo Handa has pointed out that 0a0337e0d1d1 ("mm, oom: rework oom
> detection") has subtly changed semantic for costly high order requests
> with __GFP_NOFAIL and withtout __GFP_REPEAT and those can fail right now.
> My code inspection didn't reveal any such users in the tree but it is
> true that this might lead to unexpected allocation failures and
> subsequent OOPs.
>
> __alloc_pages_slowpath wrt. GFP_NOFAIL is hard to follow currently.
> There are few special cases but we are lacking a catch all place to be
> sure we will not miss any case where the non failing allocation might
> fail. This patch reorganizes the code a bit and puts all those special
> cases under nopage label which is the generic go-to-fail path. Non
> failing allocations are retried or those that cannot retry like
> non-sleeping allocation go to the failure point directly. This should
> make the code flow much easier to follow and make it less error prone
> for future changes.
>
> While we are there we have to move the stall check up to catch
> potentially looping non-failing allocations.
>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
It's not the nicest thing that we have to duplicate all the conditions
to warn on, but it's preferable over unreliable GFP_NOFAIL handling.
Consolidating the handling of this flag makes a lot of sense to me.
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
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next prev parent reply other threads:[~2016-12-14 20:40 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-14 15:07 [PATCH] mm: consolidate GFP_NOFAIL checks in the allocator slowpath Michal Hocko
2016-12-14 20:35 ` Johannes Weiner [this message]
2016-12-15 7:54 ` Hillf Danton
2016-12-15 10:28 ` [PATCH v2] " Michal Hocko
2016-12-16 11:39 ` Tetsuo Handa
2016-12-16 11:50 ` Michal Hocko
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