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

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Message-ID: <20160225102743.GF17573@dhcp22.suse.cz>
Date:	Thu, 25 Feb 2016 11:27:44 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Nikolay Borisov <kernel@...p.com>
Cc:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	Theodore Ts'o <tytso@....edu>, 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 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@...dex-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