Re: [PATCH] mm: Use GFP_KERNEL allocation for the page cache inpage_cache_read
From: Tetsuo Handa
Date: Thu Mar 19 2015 - 07:12:54 EST
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@xxxxxxxxxxxxx
>
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