linux-kernel - Re: [PATCH RFC] ext4: use __GFP_NOFAIL in ext4_free

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Message-ID: <56CEC2EC.5000506@kyup.com>
Date:	Thu, 25 Feb 2016 11:01:32 +0200
From:	Nikolay Borisov <kernel@...p.com>
To:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	Theodore Ts'o <tytso@....edu>
Cc:	Michal Hocko <mhocko@...e.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Dmitry Monakhov <dmonakhov@...tuozzo.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH RFC] ext4: use __GFP_NOFAIL in ext4_free_blocks()



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@...dex-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?