linux-kernel - Re: [PATCHv4 26/39] ramfs: enable transparent huge page cache

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Date:	Tue, 21 May 2013 15:43:44 -0700
From:	Dave Hansen <dave@...1.net>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hillf Danton <dhillf@...il.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 26/39] ramfs: enable transparent huge page cache

On 05/11/2013 06:23 PM, Kirill A. Shutemov wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.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@...ux.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?

That seems unfortunate, and probably not something we want to
intentionally merge in this state.

Worst-case, we should at least make sure the pages remain movable in
configurations where THP-pagecache is unavailable.
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