linux-kernel - Re: [PATCH] mm: Use GFP_KERNEL allocation for the page cache inpage_cache

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Date:	Thu, 19 Mar 2015 20:11:51 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	david@...morbit.com, mhocko@...e.cz
Cc:	riel@...hat.com, akpm@...ux-foundation.org,
	viro@...iv.linux.org.uk, hannes@...xchg.org, mgorman@...e.de,
	neilb@...e.de, sage@...tank.com, mfasheh@...e.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Use GFP_KERNEL allocation for the page cache inpage_cache_read

Dave Chinner wrote:
> On Wed, Mar 18, 2015 at 03:55:28PM +0100, Michal Hocko wrote:
> > On Wed 18-03-15 10:44:11, Rik van Riel wrote:
> > > On 03/18/2015 10:09 AM, Michal Hocko wrote:
> > > > page_cache_read has been historically using page_cache_alloc_cold to
> > > > allocate a new page. This means that mapping_gfp_mask is used as the
> > > > base for the gfp_mask. Many filesystems are setting this mask to
> > > > GFP_NOFS to prevent from fs recursion issues. page_cache_read is,
> > > > however, not called from the fs layer 
> > > 
> > > Is that true for filesystems that have directories in
> > > the page cache?
> > 
> > I haven't found any explicit callers of filemap_fault except for ocfs2
> > and ceph and those seem OK to me. Which filesystems you have in mind?
> 
> Just about every major filesystem calls filemap_fault through the
> .fault callout.
> 
> C symbol: filemap_fault
> 
>   File           Function            Line
>   0 9p/vfs_file.c  <global>             831 .fault = filemap_fault,
>   1 9p/vfs_file.c  <global>             838 .fault = filemap_fault,
>   2 btrfs/file.c   <global>            2081 .fault = filemap_fault,
>   3 cifs/file.c    <global>            3242 .fault = filemap_fault,
>   4 ext4/file.c    <global>             215 .fault = filemap_fault,
>   5 f2fs/file.c    <global>              93 .fault = filemap_fault,
>   6 fuse/file.c    <global>            2062 .fault = filemap_fault,
>   7 gfs2/file.c    <global>             498 .fault = filemap_fault,
>   8 nfs/file.c     <global>             653 .fault = filemap_fault,
>   9 nilfs2/file.c  <global>             128 .fault = filemap_fault,
>   a ubifs/file.c   <global>            1536 .fault = filemap_fault,
>   b xfs/xfs_file.c <global>            1420 .fault = filemap_fault,
> 
> 
> > Btw. how would that work as we already have GFP_KERNEL allocation few
> > lines below?
> 
> GFP_KERNEL allocation for mappings is simply wrong. All mapping
> allocations where the caller cannot pass a gfp_mask need to obey
> the mapping_gfp_mask that is set by the mapping owner....
> 

Is there any chance to annotate which GFP flag needs to be used like
https://lkml.org/lkml/2015/3/17/507 ?

> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@...morbit.com
> 
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