From: Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH RFC] ext4: use __GFP_NOFAIL in ext4_free_blocks()
Date: Thu, 25 Feb 2016 11:27:44 +0100
Message-ID: <20160225102743.GF17573@dhcp22.suse.cz>
References: <20160224170912.2195.8153.stgit@buzz>
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 <20160225090839.GC17573@dhcp22.suse.cz>
 <56CEC568.6080809@kyup.com>
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Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
	Theodore Ts'o <tytso@mit.edu>, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, Dmitry Monakhov <dmonakhov@virtuozzo.com>,
	Johannes Weiner <hannes@cmpxchg.org>, linux-fsdevel@vger.kernel.org,
	linux-ext4@vger.kernel.org
To: Nikolay Borisov <kernel@kyup.com>
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On Thu 25-02-16 11:12:08, Nikolay Borisov wrote:
> 
> 
> On 02/25/2016 11:08 AM, Michal Hocko wrote:
> > On Thu 25-02-16 11:01:32, Nikolay Borisov wrote:
> >>
> >>
> >> On 02/24/2016 07:09 PM, Konstantin Khlebnikov wrote:
> >>> This might be unexpected but pages allocated for sbi->s_buddy_cache are
> >>> charged to current memory cgroup. So, GFP_NOFS allocation could fail if
> >>> current task has been killed by OOM or if current memory cgroup has no
> >>> free memory left. Block allocator cannot handle such failures here yet.
> >>>
> >>> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> >>
> >> Adding new users of GFP_NOFAIL is deprecated.
> > 
> > This is not true. GFP_NOFAIL should be used where the allocation failure
> > is no tolleratable and it is much more preferrable to doing an opencoded
> > endless loop over page allocator.
> 
> In that case the comments in buffered_rmqueue,

yes, will post the patch. The warning for order > 1 is still valid.

> and the WARN_ON in
> __alloc_pages_may_oom and __alloc_pages_slowpath perhaps should be
> removed since they are misleading?

We are only warning about absurd cases where __GFP_NOFAIL doesn't make
any sense.
-- 
Michal Hocko
SUSE Labs

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