linux-kernel - Re: [PATCH 1.2/2] mm: introduce memalloc_nofs

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Message-ID: <20160427130712.GK2179@dhcp22.suse.cz>
Date:	Wed, 27 Apr 2016 15:07:12 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Chinner <david@...morbit.com>,
	Theodore Ts'o <tytso@....edu>, Chris Mason <clm@...com>,
	Jan Kara <jack@...e.cz>, ceph-devel@...r.kernel.org,
	cluster-devel@...hat.com, linux-nfs@...r.kernel.org,
	logfs@...fs.org, xfs@....sgi.com, linux-ext4@...r.kernel.org,
	linux-btrfs@...r.kernel.org, linux-mtd@...ts.infradead.org,
	reiserfs-devel@...r.kernel.org,
	linux-ntfs-dev@...ts.sourceforge.net,
	linux-f2fs-devel@...ts.sourceforge.net,
	linux-afs@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1.2/2] mm: introduce memalloc_nofs_{save,restore} API

On Wed 27-04-16 13:54:35, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
> 

Ups missed Dave's note about:

> GFP_NOFS context is used for the following 4 reasons currently
> 	- to prevent from deadlocks when the lock held by the allocation
> 	  context would be needed during the memory reclaim
> 	- to prevent from stack overflows during the reclaim because
> 	  the allocation is performed from a deep context already
> 	- to prevent lockups when the allocation context depends on
> 	  other reclaimers to make a forward progress indirectly
> 	- just in case because this would be safe from the fs POV

	- silence lockdep false positives
-- 
Michal Hocko
SUSE Labs