linux-kernel - Re: [PATCH 1/2] mm: add PF_MEMALLOC

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Message-ID: <20160427075102.GB2179@dhcp22.suse.cz>
Date:	Wed, 27 Apr 2016 09:51:02 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Dave Chinner <david@...morbit.com>
Cc:	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	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] mm: add PF_MEMALLOC_NOFS

On Wed 27-04-16 09:07:02, Dave Chinner wrote:
> On Tue, Apr 26, 2016 at 01:56:11PM +0200, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@...e.com>
> > 
> > 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
> 
> - silencing lockdep false positives
> 
> > Introduce PF_MEMALLOC_NOFS task specific flag and memalloc_nofs_{save,restore}
> > API to control the scope. This is basically copying
> > memalloc_noio_{save,restore} API we have for other restricted allocation
> > context GFP_NOIO.
> > 
> > Xfs has already had a similar functionality as PF_FSTRANS so let's just
> > give it a more generic name and make it usable for others as well and
> > move the GFP_NOFS context tracking to the page allocator. Xfs has its
> > own accessor functions but let's keep them for now to reduce this patch
> > as minimum.
> 
> Can you split this into two patches? The first simply does this:
> 
> #define PF_MEMALLOC_NOFS PF_FSTRANS
> 
> and changes only the XFS code to use PF_MEMALLOC_NOFS.
> 
> The second patch can then do the rest of the mm API changes that we
> don't actually care about in XFS at all.  That way I can carry all
> the XFS changes in the XFS tree and not have to worry about when
> this stuff gets merged or conflicts with the rest of the work that
> is being done to the mm/ code and whatever tree that eventually
> lands in...

Sure I will do that

-- 
Michal Hocko
SUSE Labs