linux-ext4 - Re: [PATCH 2/3] mm: Only enforce stable page writes if the backing device requires it

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Date:	Thu, 1 Nov 2012 14:28:46 +0100
From:	Jan Kara <jack@...e.cz>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	axboe@...nel.dk, lucho@...kov.net, tytso@....edu, sage@...tank.com,
	ericvh@...il.com, mfasheh@...e.com, dedekind1@...il.com,
	adrian.hunter@...el.com, dhowells@...hat.com, sfrench@...ba.org,
	jlbec@...lplan.org, rminnich@...dia.gov,
	linux-cifs@...r.kernel.org, jack@...e.cz,
	martin.petersen@...cle.com, neilb@...e.de, david@...morbit.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-mtd@...ts.infradead.org, bharrosh@...asas.com,
	linux-fsdevel@...r.kernel.org,
	v9fs-developer@...ts.sourceforge.net, ceph-devel@...r.kernel.org,
	linux-ext4@...r.kernel.org, linux-afs@...ts.infradead.org,
	ocfs2-devel@....oracle.com
Subject: Re: [PATCH 2/3] mm: Only enforce stable page writes if the backing
 device requires it

On Thu 01-11-12 00:58:21, Darrick J. Wong wrote:
> Create a helper function to check if a backing device requires stable page
> writes and, if so, performs the necessary wait.  Then, make it so that all
> points in the memory manager that handle making pages writable use the helper
> function.  This should provide stable page write support to most filesystems,
> while eliminating unnecessary waiting for devices that don't require the
> feature.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> ---
>  fs/buffer.c             |    2 +-
>  fs/ext4/inode.c         |    2 +-
>  include/linux/pagemap.h |    1 +
>  mm/filemap.c            |    3 ++-
>  mm/page-writeback.c     |   11 +++++++++++
>  5 files changed, 16 insertions(+), 3 deletions(-)
> 
..
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 830893b..916dae1 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2275,3 +2275,14 @@ int mapping_tagged(struct address_space *mapping, int tag)
>  	return radix_tree_tagged(&mapping->page_tree, tag);
>  }
>  EXPORT_SYMBOL(mapping_tagged);
> +
> +void wait_on_stable_page_write(struct page *page)
> +{
> +	struct backing_dev_info *bdi = page->mapping->backing_dev_info;
> +
> +	if (!bdi_cap_stable_pages_required(bdi))
> +		return;
> +
> +	wait_on_page_writeback(page);
> +}
> +EXPORT_SYMBOL_GPL(wait_on_stable_page_write);
  Just one nit: Maybe "wait_if_stable_write()" would describe the function
better? Otherwise the patch looks OK.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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