Re: [PATCH v3 3/4] xfs: randomly fall back to near mode lookup algorithm in debug mode

Darrick J. Wong
2019-08-17T01:37:17Z

On Thu, Aug 15, 2019 at 08:55:37AM -0400, Brian Foster wrote:
> The last block scan is the dominant near mode allocation algorithm
> for a newer filesystem with fewer, large free extents. Add debug
> mode logic to randomly fall back to lookup mode to improve
> regression test coverage.

How about just using an errortag since the new sysfs interface lets
testcases / admins control the frequency?

--D

> Signed-off-by: Brian Foster <bfoster@redhat.com>
> ---
> fs/xfs/libxfs/xfs_alloc.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> index 7753b61ba532..d550aa5597bf 100644
> --- a/fs/xfs/libxfs/xfs_alloc.c
> +++ b/fs/xfs/libxfs/xfs_alloc.c
> @@ -1266,6 +1266,7 @@ xfs_alloc_ag_vextent_near(
> int i;
> xfs_agblock_t bno;
> xfs_extlen_t len;
> + bool lastblock;
>
> /* handle unitialized agbno range so caller doesn't have to */
> if (!args->min_agbno && !args->max_agbno)
> @@ -1291,7 +1292,12 @@ xfs_alloc_ag_vextent_near(
> * Otherwise run the optimized lookup search algorithm from the current
> * location to the end of the tree.
> */
> - if (xfs_btree_islastblock(acur.cnt, 0)) {
> + lastblock = xfs_btree_islastblock(acur.cnt, 0);
> +#ifdef DEBUG
> + if (lastblock)
> + lastblock = prandom_u32() & 1;
> +#endif
> + if (lastblock) {
> int j;
>
> trace_xfs_alloc_cur_lastblock(args);
> --
> 2.20.1
>