From: Nikolay Borisov <kernel@kyup.com>
Subject: Re: [PATCH RFC] ext4: use __GFP_NOFAIL in ext4_free_blocks()
Date: Thu, 25 Feb 2016 11:01:32 +0200
Message-ID: <56CEC2EC.5000506@kyup.com>
References: <20160224170912.2195.8153.stgit@buzz>
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Cc: Michal Hocko <mhocko@suse.com>, 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: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
 Theodore Ts'o <tytso@mit.edu>
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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. Where exactly does the
block allocator fail, I skimmed the code and failing ext4_mb_load_buddy
seems to be handled at all call sites. There are some BUG_ONs but from
the comments there I guess they should occur when we try to find a page
and not allocate a new one?

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