* [PATCH] mm,vmscan: don't pretend forward progress upon shrinker_rwsem contention
@ 2018-02-09 13:55 Tetsuo Handa
2018-02-13 10:13 ` Michal Hocko
0 siblings, 1 reply; 3+ messages in thread
From: Tetsuo Handa @ 2018-02-09 13:55 UTC (permalink / raw)
To: linux-mm; +Cc: Tetsuo Handa, Dave Chinner, Glauber Costa, Mel Gorman
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@I-love.SAKURA.ne.jp>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Glauber Costa <glommer@parallels.com>
Cc: Mel Gorman <mgorman@suse.de>
---
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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^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH] mm,vmscan: don't pretend forward progress upon shrinker_rwsem contention
2018-02-09 13:55 [PATCH] mm,vmscan: don't pretend forward progress upon shrinker_rwsem contention Tetsuo Handa
@ 2018-02-13 10:13 ` Michal Hocko
2018-02-20 13:29 ` Tetsuo Handa
0 siblings, 1 reply; 3+ messages in thread
From: Michal Hocko @ 2018-02-13 10:13 UTC (permalink / raw)
To: Tetsuo Handa; +Cc: linux-mm, Dave Chinner, Mel Gorman, Glauber Costa
[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@I-love.SAKURA.ne.jp>
> Cc: Dave Chinner <dchinner@redhat.com>
> Cc: Glauber Costa <glommer@parallels.com>
> Cc: Mel Gorman <mgorman@suse.de>
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@suse.ccom>
> ---
> 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
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org. For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
--
Michal Hocko
SUSE Labs
--
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^ permalink raw reply [flat|nested] 3+ messages in thread* [PATCH] mm,vmscan: don't pretend forward progress upon shrinker_rwsem contention
2018-02-13 10:13 ` Michal Hocko
@ 2018-02-20 13:29 ` Tetsuo Handa
0 siblings, 0 replies; 3+ messages in thread
From: Tetsuo Handa @ 2018-02-20 13:29 UTC (permalink / raw)
To: akpm; +Cc: linux-mm, mhocko, dchinner, mgorman, glommer
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@I-love.SAKURA.ne.jp>
Acked-by: Michal Hocko <mhocko@suse.ccom>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Glauber Costa <glommer@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
---
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
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
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^ permalink raw reply related [flat|nested] 3+ messages in thread
end of thread, other threads:[~2018-02-20 13:29 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2018-02-09 13:55 [PATCH] mm,vmscan: don't pretend forward progress upon shrinker_rwsem contention Tetsuo Handa
2018-02-13 10:13 ` Michal Hocko
2018-02-20 13:29 ` Tetsuo Handa
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