[PATCH] mm: vmscan: fix memcg-aware shrinkers not called on global reclaim

[PATCH] mm: vmscan: fix memcg-aware shrinkers not called on global reclaim

[Vladimir Davydov]

We must call shrink_slab() for each memory cgroup on both global and
memcg reclaim in shrink_node_memcg(). Commit d71df22b55099 accidentally
changed that so that now shrink_slab() is only called with memcg != NULL
on memcg reclaim. As a result, memcg-aware shrinkers (including
dentry/inode) are never invoked on global reclaim. Fix that.

Fixes: d71df22b55099 ("mm, vmscan: begin reclaiming pages on a per-node basis")
Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
---
 mm/vmscan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 650d26832569..374d95d04178 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2561,7 +2561,7 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
 			shrink_node_memcg(pgdat, memcg, sc, &lru_pages);
 			node_lru_pages += lru_pages;
 
-			if (!global_reclaim(sc))
+			if (memcg)
 				shrink_slab(sc->gfp_mask, pgdat->node_id,
 					    memcg, sc->nr_scanned - scanned,
 					    lru_pages);
-- 
2.1.4

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Re: [PATCH] mm: vmscan: fix memcg-aware shrinkers not called on global reclaim

[Michal Hocko]

On Mon 01-08-16 16:03:10, Vladimir Davydov wrote:
> We must call shrink_slab() for each memory cgroup on both global and
> memcg reclaim in shrink_node_memcg(). Commit d71df22b55099 accidentally
> changed that so that now shrink_slab() is only called with memcg != NULL
> on memcg reclaim. As a result, memcg-aware shrinkers (including
> dentry/inode) are never invoked on global reclaim. Fix that.
> 
> Fixes: d71df22b55099 ("mm, vmscan: begin reclaiming pages on a per-node basis")

I guess you meant b2e18757f2c9. I do not see d71df22b55099 anywhere.

> Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>

The fix looks ok to me otherwise

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  mm/vmscan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 650d26832569..374d95d04178 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2561,7 +2561,7 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
>  			shrink_node_memcg(pgdat, memcg, sc, &lru_pages);
>  			node_lru_pages += lru_pages;
>  
> -			if (!global_reclaim(sc))
> +			if (memcg)
>  				shrink_slab(sc->gfp_mask, pgdat->node_id,
>  					    memcg, sc->nr_scanned - scanned,
>  					    lru_pages);
> -- 
> 2.1.4
> 
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Michal Hocko
SUSE Labs

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Re: [PATCH] mm: vmscan: fix memcg-aware shrinkers not called on global reclaim

[Vladimir Davydov]

On Mon, Aug 01, 2016 at 03:18:40PM +0200, Michal Hocko wrote:
> On Mon 01-08-16 16:03:10, Vladimir Davydov wrote:
> > We must call shrink_slab() for each memory cgroup on both global and
> > memcg reclaim in shrink_node_memcg(). Commit d71df22b55099 accidentally
> > changed that so that now shrink_slab() is only called with memcg != NULL
> > on memcg reclaim. As a result, memcg-aware shrinkers (including
> > dentry/inode) are never invoked on global reclaim. Fix that.
> > 
> > Fixes: d71df22b55099 ("mm, vmscan: begin reclaiming pages on a per-node basis")
> 
> I guess you meant b2e18757f2c9. I do not see d71df22b55099 anywhere.

I'm basing on top of v4.7-mmotm-2016-07-28-16-33 and there it's
d71df22b55099.

> 
> > Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
> 
> The fix looks ok to me otherwise
> 
> Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

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Re: [PATCH] mm: vmscan: fix memcg-aware shrinkers not called on global reclaim

[Michal Hocko]

On Mon 01-08-16 16:21:45, Vladimir Davydov wrote:
> On Mon, Aug 01, 2016 at 03:18:40PM +0200, Michal Hocko wrote:
> > On Mon 01-08-16 16:03:10, Vladimir Davydov wrote:
> > > We must call shrink_slab() for each memory cgroup on both global and
> > > memcg reclaim in shrink_node_memcg(). Commit d71df22b55099 accidentally
> > > changed that so that now shrink_slab() is only called with memcg != NULL
> > > on memcg reclaim. As a result, memcg-aware shrinkers (including
> > > dentry/inode) are never invoked on global reclaim. Fix that.
> > > 
> > > Fixes: d71df22b55099 ("mm, vmscan: begin reclaiming pages on a per-node basis")
> > 
> > I guess you meant b2e18757f2c9. I do not see d71df22b55099 anywhere.
> 
> I'm basing on top of v4.7-mmotm-2016-07-28-16-33 and there it's
> d71df22b55099.

But this sha is unstable. THe patch you are referring to is already
sitting in the Linus tree so please use his (stable sha instead).
-- 
Michal Hocko
SUSE Labs

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Re: [PATCH] mm: vmscan: fix memcg-aware shrinkers not called on global reclaim

[Johannes Weiner]

On Mon, Aug 01, 2016 at 04:03:10PM +0300, Vladimir Davydov wrote:
> We must call shrink_slab() for each memory cgroup on both global and
> memcg reclaim in shrink_node_memcg(). Commit d71df22b55099 accidentally
> changed that so that now shrink_slab() is only called with memcg != NULL
> on memcg reclaim. As a result, memcg-aware shrinkers (including
> dentry/inode) are never invoked on global reclaim. Fix that.
> 
> Fixes: d71df22b55099 ("mm, vmscan: begin reclaiming pages on a per-node basis")
> Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>

Ouch, I missed that in the review. The change looked so obviously
correct, but the shrink_slab() interface is a little deceiving. It
would be great if shrink_slab() could handle root_mem_cgroup/NULL and
then we'd always call it from inside the loop. But AFAICS we need the
global call to get the cumulative scanned/lru_pages ratio from all of
the memcgs reclaimed... grr. Oh well.

This fix looks correct to me, anyway.

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

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Re: [PATCH] mm: vmscan: fix memcg-aware shrinkers not called on global reclaim

[Minchan Kim]

On Mon, Aug 01, 2016 at 04:03:10PM +0300, Vladimir Davydov wrote:
> We must call shrink_slab() for each memory cgroup on both global and
> memcg reclaim in shrink_node_memcg(). Commit d71df22b55099 accidentally
> changed that so that now shrink_slab() is only called with memcg != NULL
> on memcg reclaim. As a result, memcg-aware shrinkers (including
> dentry/inode) are never invoked on global reclaim. Fix that.
> 
> Fixes: d71df22b55099 ("mm, vmscan: begin reclaiming pages on a per-node basis")
> Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: Minchan Kim <minchan@kernel.org>

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Re: [PATCH] mm: vmscan: fix memcg-aware shrinkers not called on global reclaim

[Mel Gorman]

On Mon, Aug 01, 2016 at 04:03:10PM +0300, Vladimir Davydov wrote:
> We must call shrink_slab() for each memory cgroup on both global and
> memcg reclaim in shrink_node_memcg(). Commit d71df22b55099 accidentally
> changed that so that now shrink_slab() is only called with memcg != NULL
> on memcg reclaim. As a result, memcg-aware shrinkers (including
> dentry/inode) are never invoked on global reclaim. Fix that.
> 
> Fixes: d71df22b55099 ("mm, vmscan: begin reclaiming pages on a per-node basis")
> Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>

Acked-by: Mel Gorman <mgorman@techsingularity.net>

-- 
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SUSE Labs

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