Re: [PATCH 1/5] ext4: Make mballoc try target group first even with mb_optimize_scan

Jan Kara
2022-09-26T09:11:36Z

On Thu 22-09-22 11:15:42, Jan Kara wrote:
> On Wed 21-09-22 22:52:34, Theodore Ts'o wrote:
> > On Thu, 8 Sep 2022 11:21:24 +0200, Jan Kara wrote:
> > > One of the side-effects of mb_optimize_scan was that the optimized
> > > functions to select next group to try were called even before we tried
> > > the goal group. As a result we no longer allocate files close to
> > > corresponding inodes as well as we don't try to expand currently
> > > allocated extent in the same group. This results in reaim regression
> > > with workfile.disk workload of upto 8% with many clients on my test
> > > machine:
> > >
> > > [...]
> >
> > Applied, thanks!
> >
> > [1/5] ext4: Make mballoc try target group first even with mb_optimize_scan
> > commit: 4fca50d440cc5d4dc570ad5484cc0b70b381bc2a
> > [2/5] ext4: Avoid unnecessary spreading of allocations among groups
> > commit: 1940265ede6683f6317cba0d428ce6505eaca944
> > [3/5] ext4: Make directory inode spreading reflect flexbg size
> > commit: 613c5a85898d1cd44e68f28d65eccf64a8ace9cf
> > [4/5] ext4: Use locality group preallocation for small closed files
> > commit: a9f2a2931d0e197ab28c6007966053fdababd53f
> > [5/5] ext4: Use buckets for cr 1 block scan instead of rbtree
> > commit: 83e80a6e3543f37f74c8e48a5f305b054b65ce2a
>
> Thanks Ted! I just have locally a small fixup to the series that was reported
> by Smatch. It is attached, either fold it into the last patch or just merge
> it as a separate patch. Thanks!

Ted, I've noticed you've merged my mballoc fixes (and pushed them to Linus)
without this fixup. Can you please merge it? The use of uninitialized
variable seems rare but possible...

Honza

> From 8885b11fb253e08ecfa90a28beffb01719af84f5 Mon Sep 17 00:00:00 2001
> From: Jan Kara <jack@suse.cz>
> Date: Thu, 22 Sep 2022 11:09:29 +0200
> Subject: [PATCH] ext4: Fixup possible uninitialized variable access in
> ext4_mb_choose_next_group_cr1()
>
> Variable 'grp' may be left uninitialized if there's no group with
> suitable average fragment size (or larger). Fix the problem by
> initializing it earlier.
>
> Fixes: 83e80a6e3543 ("ext4: use buckets for cr 1 block scan instead of rbtree")
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
> fs/ext4/mballoc.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 71f5b67d7f28..9dad93059945 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -910,7 +910,7 @@ static void ext4_mb_choose_next_group_cr1(struct ext4_allocation_context *ac,
> int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
> {
> struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
> - struct ext4_group_info *grp, *iter;
> + struct ext4_group_info *grp = NULL, *iter;
> int i;
>
> if (unlikely(ac->ac_flags & EXT4_MB_CR1_OPTIMIZED)) {
> @@ -927,7 +927,6 @@ static void ext4_mb_choose_next_group_cr1(struct ext4_allocation_context *ac,
> read_unlock(&sbi->s_mb_avg_fragment_size_locks[i]);
> continue;
> }
> - grp = NULL;
> list_for_each_entry(iter, &sbi->s_mb_avg_fragment_size[i],
> bb_avg_fragment_size_node) {
> if (sbi->s_mb_stats)
> --
> 2.35.3
>

--
Jan Kara <jack@suse.com>
SUSE Labs, CR