On Wed, 2011-09-28 at 11:09 +0800, Shaohua Li wrote:
> On Mon, 2011-09-26 at 17:45 +0800, Christoph Hellwig wrote:
> > On Mon, Sep 26, 2011 at 03:38:47PM +0800, Shaohua Li wrote:
> > > On Mon, 2011-09-26 at 15:30 +0800, Christoph Hellwig wrote:
> > > > On Mon, Sep 26, 2011 at 10:30:26AM +0800, Shaohua Li wrote:
> > > > > Some filesystems implement .writepages. We don't have blk plug
> > > > > in such filesystems for .writepages.
> > > >
> > > > Please add the plugging in the actual ->writepages instances.
> > > there are several filesystems have ->writepages. Can you share an hint
> > > why we don't add plugging in the do_writepages?
> >
> > Because do_writepages is completely generic code with no knowledge of
> > block I/O. I really don't want to have block plugging be intimately
> > tied into core VM/writeback code all over. We've been there with
> > ->sync_page, and it was a major pain - nevermind the additional (small)
> > overhead for the not block based filesystems.
> I searched a little bit, looks only ext4 need it. here is the patch.
>
>
> Add block plug for ext4 .writepages. Though ext4 .writepages
> already handles request merge very well, block plug is still
> helpful to reduce block lock contention.
>
ping
> Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx>
>
> ---
> fs/ext4/inode.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> Index: linux/fs/ext4/inode.c
> ===================================================================
> --- linux.orig/fs/ext4/inode.c 2011-09-28 10:13:50.000000000 +0800
> +++ linux/fs/ext4/inode.c 2011-09-28 10:23:31.000000000 +0800
> @@ -2046,6 +2046,7 @@ static int ext4_da_writepages(struct add
> struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);
> pgoff_t done_index = 0;
> pgoff_t end;
> + struct blk_plug plug;
>
> trace_ext4_da_writepages(inode, wbc);
>
> @@ -2124,6 +2125,7 @@ retry:
> if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
> tag_pages_for_writeback(mapping, index, end);
>
> + blk_start_plug(&plug);
> while (!ret && wbc->nr_to_write > 0) {
>
> /*
> @@ -2188,6 +2190,7 @@ retry:
> */
> break;
> }
> + blk_finish_plug(&plug);
> if (!io_done && !cycled) {
> cycled = 1;
> index = 0;
>
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