Re: [PATCH 6/9] mm: vmscan: use per memcg nr_deferred of shrinker

[Yang Shi]

On Wed, Dec 2, 2020 at 7:08 PM Roman Gushchin <guro@xxxxxx> wrote:
>
> On Wed, Dec 02, 2020 at 10:27:22AM -0800, Yang Shi wrote:
> > Use per memcg's nr_deferred for memcg aware shrinkers.  The shrinker's nr_deferred
> > will be used in the following cases:
> >     1. Non memcg aware shrinkers
> >     2. !CONFIG_MEMCG
> >     3. memcg is disabled by boot parameter
> >
> > Signed-off-by: Yang Shi <shy828301@xxxxxxxxx>
> > ---
> >  mm/vmscan.c | 88 +++++++++++++++++++++++++++++++++++++++++++++++++----
> >  1 file changed, 82 insertions(+), 6 deletions(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index cba0bc8d4661..d569fdcaba79 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -203,6 +203,12 @@ static DECLARE_RWSEM(shrinker_rwsem);
> >  static DEFINE_IDR(shrinker_idr);
> >  static int shrinker_nr_max;
> >
> > +static inline bool is_deferred_memcg_aware(struct shrinker *shrinker)
> > +{
> > +     return (shrinker->flags & SHRINKER_MEMCG_AWARE) &&
> > +             !mem_cgroup_disabled();
> > +}
> > +
> >  static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> >  {
> >       int id, ret = -ENOMEM;
> > @@ -271,7 +277,58 @@ static bool writeback_throttling_sane(struct scan_control *sc)
> >  #endif
> >       return false;
> >  }
> > +
> > +static inline long count_nr_deferred(struct shrinker *shrinker,
> > +                                  struct shrink_control *sc)
> > +{
> > +     bool per_memcg_deferred = is_deferred_memcg_aware(shrinker) && sc->memcg;
> > +     struct memcg_shrinker_deferred *deferred;
> > +     struct mem_cgroup *memcg = sc->memcg;
> > +     int nid = sc->nid;
> > +     int id = shrinker->id;
> > +     long nr;
> > +
> > +     if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
> > +             nid = 0;
> > +
> > +     if (per_memcg_deferred) {
> > +             deferred = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_deferred,
> > +                                                  true);
> > +             nr = atomic_long_xchg(&deferred->nr_deferred[id], 0);
> > +     } else
> > +             nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
> > +
> > +     return nr;
> > +}
> > +
> > +static inline long set_nr_deferred(long nr, struct shrinker *shrinker,
> > +                                struct shrink_control *sc)
> > +{
> > +     bool per_memcg_deferred = is_deferred_memcg_aware(shrinker) && sc->memcg;
> > +     struct memcg_shrinker_deferred *deferred;
> > +     struct mem_cgroup *memcg = sc->memcg;
> > +     int nid = sc->nid;
> > +     int id = shrinker->id;
> > +     long new_nr;
> > +
> > +     if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
> > +             nid = 0;
> > +
> > +     if (per_memcg_deferred) {
> > +             deferred = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_deferred,
> > +                                                  true);
> > +             new_nr = atomic_long_add_return(nr, &deferred->nr_deferred[id]);
> > +     } else
> > +             new_nr = atomic_long_add_return(nr, &shrinker->nr_deferred[nid]);
> > +
> > +     return new_nr;
> > +}
> >  #else
> > +static inline bool is_deferred_memcg_aware(struct shrinker *shrinker)
> > +{
> > +     return false;
> > +}
> > +
> >  static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> >  {
> >       return 0;
> > @@ -290,6 +347,29 @@ static bool writeback_throttling_sane(struct scan_control *sc)
> >  {
> >       return true;
> >  }
> > +
> > +static inline long count_nr_deferred(struct shrinker *shrinker,
> > +                                  struct shrink_control *sc)
> > +{
> > +     int nid = sc->nid;
> > +
> > +     if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
> > +             nid = 0;
> > +
> > +     return atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
> > +}
> > +
> > +static inline long set_nr_deferred(long nr, struct shrinker *shrinker,
> > +                                struct shrink_control *sc)
> > +{
> > +     int nid = sc->nid;
> > +
> > +     if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
> > +             nid = 0;
> > +
> > +     return atomic_long_add_return(nr,
> > +                                   &shrinker->nr_deferred[nid]);
> > +}
> >  #endif
> >
> >  /*
> > @@ -429,13 +509,10 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> >       long freeable;
> >       long nr;
> >       long new_nr;
> > -     int nid = shrinkctl->nid;
> >       long batch_size = shrinker->batch ? shrinker->batch
> >                                         : SHRINK_BATCH;
> >       long scanned = 0, next_deferred;
> >
> > -     if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
> > -             nid = 0;
> >
> >       freeable = shrinker->count_objects(shrinker, shrinkctl);
> >       if (freeable == 0 || freeable == SHRINK_EMPTY)
> > @@ -446,7 +523,7 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> >        * and zero it so that other concurrent shrinker invocations
> >        * don't also do this scanning work.
> >        */
> > -     nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
> > +     nr = count_nr_deferred(shrinker, shrinkctl);
> >
> >       total_scan = nr;
> >       if (shrinker->seeks) {
> > @@ -539,8 +616,7 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> >        * move the unused scan count back into the shrinker in a
> >        * manner that handles concurrent updates.
> >        */
> > -     new_nr = atomic_long_add_return(next_deferred,
> > -                                     &shrinker->nr_deferred[nid]);
> > +     new_nr = set_nr_deferred(next_deferred, shrinker, shrinkctl);
>
> Ok, I think patch (1) can be just merged into this and then it would make total sense.

Sure. Makes sense to me.