On Mon 08-01-18 10:00:42, Jiang Biao wrote:
> When running ltp stress test for 7*24 hours, vmscan occasionally emits the
> following warning continuously:
>
> mb_cache_scan+0x0/0x3f0 negative objects to delete
> nr=-9232265467809300450
> ....
>
> Trace info shows the freeable(mb_cache_count returns) is -1, which causes
> the continuous accumulation and overflow of total_scan.
>
> This patch makes sure that mb_cache_count() not return a negative value,
> which makes the mbcache shrinker more robust.
Thanks for the patch. Couple of comments below.
> Signed-off-by: Jiang Biao <jiang.biao2@xxxxxxxxxx>
> CC: "Theodore Ts'o" <tytso@xxxxxxx>
> CC: Eric Biggers <ebiggers@xxxxxxxxxx>
> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> CC: Jan Kara <jack@xxxxxxx>
> ---
> fs/mbcache.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/mbcache.c b/fs/mbcache.c
> index b8b8b9c..c758458 100644
> --- a/fs/mbcache.c
> +++ b/fs/mbcache.c
> @@ -238,7 +238,9 @@ void mb_cache_entry_delete(struct mb_cache *cache, u32 key, u64 value)
> spin_lock(&cache->c_list_lock);
> if (!list_empty(&entry->e_list)) {
> list_del_init(&entry->e_list);
> - cache->c_entry_count--;
> + /*Make sure c_entry_count is not zero before dec*/
The comment is useless, just delete it.
> + if (cache->c_entry_count != 0)
cache->c_entry_count > 0 would be more logical...
> + cache->c_entry_count--;
OK, but please also add:
else
WARN_ONCE(1, "mbcache: Entry count "
"going negative!");
Also as I said in another email I'd be actually more interested in
debugging how can entry count go to such huge value rather than trying to
paper over it...
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
