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From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Dave Hansen <dave@sr71.net>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>, Hugh Dickins <hughd@google.com>,
        Wu Fengguang <fengguang.wu@intel.com>, Jan Kara <jack@suse.cz>,
        Mel Gorman <mgorman@suse.de>, linux-mm@kvack.org,
        Andi Kleen <ak@linux.intel.com>,
        Matthew Wilcox <matthew.r.wilcox@intel.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Hillf Danton <dhillf@gmail.com>, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org
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Subject: Re: [PATCHv4 26/39] ramfs: enable transparent huge page cache
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Date: Wed, 22 May 2013 17:22:36 +0300 (EEST)
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Dave Hansen wrote:
> On 05/11/2013 06:23 PM, Kirill A. Shutemov wrote:
> > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> > 
> > ramfs is the most simple fs from page cache point of view. Let's start
> > transparent huge page cache enabling here.
> > 
> > For now we allocate only non-movable huge page. ramfs pages cannot be
> > moved yet.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > ---
> >  fs/ramfs/inode.c |    6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/ramfs/inode.c b/fs/ramfs/inode.c
> > index c24f1e1..54d69c7 100644
> > --- a/fs/ramfs/inode.c
> > +++ b/fs/ramfs/inode.c
> > @@ -61,7 +61,11 @@ struct inode *ramfs_get_inode(struct super_block *sb,
> >  		inode_init_owner(inode, dir, mode);
> >  		inode->i_mapping->a_ops = &ramfs_aops;
> >  		inode->i_mapping->backing_dev_info = &ramfs_backing_dev_info;
> > -		mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
> > +		/*
> > +		 * TODO: make ramfs pages movable
> > +		 */
> > +		mapping_set_gfp_mask(inode->i_mapping,
> > +				GFP_TRANSHUGE & ~__GFP_MOVABLE);
> 
> So, before these patches, ramfs was movable.  Now, even on architectures
> or configurations that have no chance of using THP-pagecache, ramfs
> pages are no longer movable.  Right?

No, it wasn't movable. GFP_HIGHUSER is not GFP_HIGHUSER_MOVABLE (yeah,
names of gfp constants could be more consistent).

ramfs should be fixed to use movable pages, but it's outside the scope of the
patchset.

See more details: http://lkml.org/lkml/2013/4/2/720

-- 
 Kirill A. Shutemov