On Fri, 25 Mar 2011 16:25:57 -0400
Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> Commit 522440ed made cifs set backing_dev_info on the mapping attached
> to new inodes. This change caused a fairly significant read performance
> regression, as cifs started doing page-sized reads exclusively.
>
> By virtue of the fact that they're allocated as part of cifs_sb_info by
> kzalloc, the ra_pages on cifs BDIs get set to 0, which prevents any
> readahead. This forces the normal read codepaths to use readpage instead
> of readpages causing a four-fold increase in the number of read calls
> with the default rsize.
>
> Fix it by setting ra_pages in the BDI to the same value as that in the
> default_backing_dev_info.
>
> Cc: stable@xxxxxxxxxx
> Reported-and-Tested-by: Till <till2.schaefer@xxxxxxxxxxxxxxx>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
> fs/cifs/cifsfs.c | 1 +
> 1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
> index 1af2470..fb6a2ad 100644
> --- a/fs/cifs/cifsfs.c
> +++ b/fs/cifs/cifsfs.c
> @@ -131,6 +131,7 @@ cifs_read_super(struct super_block *sb, void *data,
> kfree(cifs_sb);
> return rc;
> }
> + cifs_sb->bdi.ra_pages = default_backing_dev_info.ra_pages;
>
> #ifdef CONFIG_CIFS_DFS_UPCALL
> /* copy mount params to sb for use in submounts */
Forgot to mention that this fixes the following kernel.org bug:
https://bugzilla.kernel.org/show_bug.cgi?id=31662
...look there if you're curious about the gory details...
--
Jeff Layton <jlayton@xxxxxxxxxx>
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