[Fixup Vladimir's email and drop the stable mailing list]
On Wed 12-10-16 09:09:49, Shaohua Li wrote:
> Our system uses significantly more slab memory with memcg enabled with
> latest kernel. With 3.10 kernel, slab uses 2G memory, while with 4.6
> kernel, 6G memory is used. Looks the shrinker has problem. Let's see we
> have two memcg for one shrinker. In do_shrink_slab:
>
> 1. Check cg1. nr_deferred = 0, assume total_scan = 700. batch size is 1024,
> then no memory is freed. nr_deferred = 700
> 2. Check cg2. nr_deferred = 700. Assume freeable = 20, then total_scan = 10
> or 40. Let's assume it's 10. No memory is freed. nr_deferred = 10.
>
> The deferred share of cg1 is lost in this case. kswapd will free no
> memory even run above steps again and again.
>
> The fix makes sure one memcg's deferred share isn't lost.
>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx (v4.0+)
> Signed-off-by: Shaohua Li <shli@xxxxxx>
> ---
> mm/vmscan.c | 14 +++++++++++---
> 1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 0fe8b71..c3822ae 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -291,6 +291,7 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> int nid = shrinkctl->nid;
> long batch_size = shrinker->batch ? shrinker->batch
> : SHRINK_BATCH;
> + long scanned = 0, next_deferred;
>
> freeable = shrinker->count_objects(shrinker, shrinkctl);
> if (freeable == 0)
> @@ -312,7 +313,9 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> pr_err("shrink_slab: %pF negative objects to delete nr=%ld\n",
> shrinker->scan_objects, total_scan);
> total_scan = freeable;
> - }
> + next_deferred = nr;
> + } else
> + next_deferred = total_scan;
>
> /*
> * We need to avoid excessive windup on filesystem shrinkers
> @@ -369,17 +372,22 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
>
> count_vm_events(SLABS_SCANNED, nr_to_scan);
> total_scan -= nr_to_scan;
> + scanned += nr_to_scan;
>
> cond_resched();
> }
>
> + if (next_deferred >= scanned)
> + next_deferred -= scanned;
> + else
> + next_deferred = 0;
> /*
> * move the unused scan count back into the shrinker in a
> * manner that handles concurrent updates. If we exhausted the
> * scan, there is no need to do an update.
> */
> - if (total_scan > 0)
> - new_nr = atomic_long_add_return(total_scan,
> + if (next_deferred > 0)
> + new_nr = atomic_long_add_return(next_deferred,
> &shrinker->nr_deferred[nid]);
> else
> new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);
> --
> 2.9.3
>
> --
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--
Michal Hocko
SUSE Labs
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