Re: [v6 PATCH 08/11] mm: vmscan: use per memcg nr_deferred of shrinker

[Yang Shi]

On Thu, Feb 4, 2021 at 12:42 AM Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> wrote:
>
> On 03.02.2021 20:20, 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 | 94 +++++++++++++++++++++++++++++++++++++++++++----------
> >  1 file changed, 77 insertions(+), 17 deletions(-)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index d9126f12890f..545422d2aeec 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -190,6 +190,13 @@ static int shrinker_nr_max;
> >  #define NR_MAX_TO_SHR_MAP_SIZE(nr_max) \
> >       (DIV_ROUND_UP(nr_max, BITS_PER_LONG) * sizeof(unsigned long))
> >
> > +static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
> > +                                                  int nid)
> > +{
> > +     return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
> > +                                      lockdep_is_held(&shrinker_rwsem));
> > +}
>
> Thanks for the helper. Why not to introduce and become to use it in old places
> in a separate patch?

What do you mean about "old places"? Where was it introduced in v5 (in
patch #10)?

>
> > +
> >  static void free_shrinker_info_rcu(struct rcu_head *head)
> >  {
> >       kvfree(container_of(head, struct shrinker_info, rcu));
> > @@ -204,8 +211,7 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
> >       int size = m_size + d_size;
> >
> >       for_each_node(nid) {
> > -             old = rcu_dereference_protected(
> > -                     mem_cgroup_nodeinfo(memcg, nid)->shrinker_info, true);
> > +             old = shrinker_info_protected(memcg, nid);
> >               /* Not yet online memcg */
> >               if (!old)
> >                       return 0;
> > @@ -239,7 +245,7 @@ void free_shrinker_info(struct mem_cgroup *memcg)
> >
> >       for_each_node(nid) {
> >               pn = mem_cgroup_nodeinfo(memcg, nid);
> > -             info = rcu_dereference_protected(pn->shrinker_info, true);
> > +             info = shrinker_info_protected(memcg, nid);
> >               kvfree(info);
> >               rcu_assign_pointer(pn->shrinker_info, NULL);
> >       }
> > @@ -358,6 +364,25 @@ static void unregister_memcg_shrinker(struct shrinker *shrinker)
> >       up_write(&shrinker_rwsem);
> >  }
> >
> > +
> > +static long count_nr_deferred_memcg(int nid, struct shrinker *shrinker,
> > +                                 struct mem_cgroup *memcg)
> > +{
> > +     struct shrinker_info *info;
> > +
> > +     info = shrinker_info_protected(memcg, nid);
> > +     return atomic_long_xchg(&info->nr_deferred[shrinker->id], 0);
> > +}
> > +
> > +static long set_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
> > +                               struct mem_cgroup *memcg)
> > +{
> > +     struct shrinker_info *info;
> > +
> > +     info = shrinker_info_protected(memcg, nid);
> > +     return atomic_long_add_return(nr, &info->nr_deferred[shrinker->id]);
> > +}
>
> Names confuse me a little bit. What about xchg_nr_deferred_memcg() and add_nr_deferred_memcg()?

add_nr_deferred_memcg() sounds more self-explained to me.

>
> >  static bool cgroup_reclaim(struct scan_control *sc)
> >  {
> >       return sc->target_mem_cgroup;
> > @@ -396,6 +421,18 @@ static void unregister_memcg_shrinker(struct shrinker *shrinker)
> >  {
> >  }
> >
> > +static long count_nr_deferred_memcg(int nid, struct shrinker *shrinker,
> > +                                 struct mem_cgroup *memcg)
> > +{
> > +     return 0;
> > +}
> > +
> > +static long set_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
> > +                               struct mem_cgroup *memcg)
> > +{
> > +     return 0;
> > +}
> > +
> >  static bool cgroup_reclaim(struct scan_control *sc)
> >  {
> >       return false;
> > @@ -407,6 +444,39 @@ static bool writeback_throttling_sane(struct scan_control *sc)
> >  }
> >  #endif
> >
> > +static long count_nr_deferred(struct shrinker *shrinker,
> > +                           struct shrink_control *sc)
> > +{
> > +     int nid = sc->nid;
> > +
> > +     if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
> > +             nid = 0;
> > +
> > +     if (sc->memcg &&
> > +         (shrinker->flags & SHRINKER_MEMCG_AWARE))
> > +             return count_nr_deferred_memcg(nid, shrinker,
> > +                                            sc->memcg);
> > +
> > +     return atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
> > +}
> > +
> > +
> > +static 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;
> > +
> > +     if (sc->memcg &&
> > +         (shrinker->flags & SHRINKER_MEMCG_AWARE))
> > +             return set_nr_deferred_memcg(nr, nid, shrinker,
> > +                                          sc->memcg);
> > +
> > +     return atomic_long_add_return(nr, &shrinker->nr_deferred[nid]);
> > +}
> > +
> >  /*
> >   * This misses isolated pages which are not accounted for to save counters.
> >   * As the data only determines if reclaim or compaction continues, it is
> > @@ -539,14 +609,10 @@ 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)
> >               return freeable;
> > @@ -556,7 +622,7 @@ 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) {
> > @@ -647,14 +713,9 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
> >               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.
> > +      * manner that handles concurrent updates.
> >        */
> > -     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]);
> > +     new_nr = set_nr_deferred(next_deferred, shrinker, shrinkctl);
> >
> >       trace_mm_shrink_slab_end(shrinker, shrinkctl->nid, freed, nr, new_nr, total_scan);
> >       return freed;
> > @@ -674,8 +735,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
> >       if (!down_read_trylock(&shrinker_rwsem))
> >               return 0;
> >
> > -     info = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
> > -                                      true);
> > +     info = shrinker_info_protected(memcg, nid);
> >       if (unlikely(!info))
> >               goto unlock;
> >
> >
>
>