On Fri, Feb 5, 2021 at 6:42 AM Kirill Tkhai [off-list ref] wrote:

On 04.02.2021 20:23, Yang Shi wrote:

quoted

On Thu, Feb 4, 2021 at 12:42 AM Kirill Tkhai [off-list ref] wrote:

quoted

On 03.02.2021 20:20, Yang Shi wrote:

quoted

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 <redacted>
---
 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)?

I mean existing places touched by this patch, which became to use the new helper
in this patch: free_shrinker_info(), expand_one_shrinker_info(), shrink_slab_memcg().

Aha, I see. So, you mean add the helper before in a separate patch.
Right after patch #5 (which rename shrinker_map to shrinker_info)
should be a good place.

quoted

quoted

quoted

+
 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.

quoted

quoted

 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;