[Fix Glauber's email]
On Fri 09-02-18 22:55:44, Tetsuo Handa wrote:
> Since we no longer use return value of shrink_slab() for normal reclaim,
> the comment is no longer true. If some do_shrink_slab() call takes
> unexpectedly long (root cause of stall is currently unknown) when
> register_shrinker()/unregister_shrinker() is pending, trying to drop
> caches via /proc/sys/vm/drop_caches could become infinite cond_resched()
> loop if many mem_cgroup are defined. For safety, let's not pretend forward
> progress.
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: Dave Chinner <dchinner@xxxxxxxxxx>
> Cc: Glauber Costa <glommer@xxxxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
Yes, this makes sense to me. The whole "let's pretend we made some
progress" was an ugly hack IMHO.
Acked-by: Michal Hocko <mhocko@xxxxxxxxx>
> ---
> mm/vmscan.c | 10 +---------
> 1 file changed, 1 insertion(+), 9 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 4447496..17da5a5 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -442,16 +442,8 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
> if (memcg && (!memcg_kmem_enabled() || !mem_cgroup_online(memcg)))
> return 0;
>
> - if (!down_read_trylock(&shrinker_rwsem)) {
> - /*
> - * If we would return 0, our callers would understand that we
> - * have nothing else to shrink and give up trying. By returning
> - * 1 we keep it going and assume we'll be able to shrink next
> - * time.
> - */
> - freed = 1;
> + if (!down_read_trylock(&shrinker_rwsem))
> goto out;
> - }
>
> list_for_each_entry(shrinker, &shrinker_list, list) {
> struct shrink_control sc = {
> --
> 1.8.3.1
>
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--
Michal Hocko
SUSE Labs
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