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SubjectRe: [v6 PATCH 08/11] mm: vmscan: use per memcg nr_deferred of shrinker
On Thu, Feb 4, 2021 at 12:42 AM Kirill Tkhai <ktkhai@virtuozzo.com> 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@gmail.com>
> > ---
> > 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;
> >
> >
>
>

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