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

> +
> 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()?

> 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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