mm: vmscan: add shrinker_srcu_generation

After we make slab shrink lockless with SRCU, the longest sleep
unregister_shrinker() will be a sleep waiting for all do_shrink_slab()
calls.

To avoid long unbreakable action in the unregister_shrinker(), add
shrinker_srcu_generation to restore a check similar to the
rwsem_is_contendent() check that we had before.

And for memcg slab shrink, we unlock SRCU and continue iterations from the
next shrinker id.

Link: https://lkml.kernel.org/r/20230313112819.38938-5-zhengqi.arch@bytedance.com
Signed-off-by: Kirill Tkhai <tkhai@ya.ru>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Christian König <christian.koenig@amd.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Sultan Alsawaf <sultan@kerneltoast.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index ce78340..5c2a224 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -204,6 +204,7 @@ static void set_task_reclaim_state(struct task_struct *task,
 LIST_HEAD(shrinker_list);
 DECLARE_RWSEM(shrinker_rwsem);
 DEFINE_SRCU(shrinker_srcu);
+static atomic_t shrinker_srcu_generation = ATOMIC_INIT(0);
 
 #ifdef CONFIG_MEMCG
 static int shrinker_nr_max;
@@ -776,6 +777,7 @@ void unregister_shrinker(struct shrinker *shrinker)
        debugfs_entry = shrinker_debugfs_remove(shrinker);
        up_write(&shrinker_rwsem);
 
+       atomic_inc(&shrinker_srcu_generation);
        synchronize_srcu(&shrinker_srcu);
 
        debugfs_remove_recursive(debugfs_entry);
@@ -797,6 +799,7 @@ void synchronize_shrinkers(void)
 {
        down_write(&shrinker_rwsem);
        up_write(&shrinker_rwsem);
+       atomic_inc(&shrinker_srcu_generation);
        synchronize_srcu(&shrinker_srcu);
 }
 EXPORT_SYMBOL(synchronize_shrinkers);
@@ -906,18 +909,20 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 {
        struct shrinker_info *info;
        unsigned long ret, freed = 0;
-       int srcu_idx;
-       int i;
+       int srcu_idx, generation;
+       int i = 0;
 
        if (!mem_cgroup_online(memcg))
                return 0;
 
+again:
        srcu_idx = srcu_read_lock(&shrinker_srcu);
        info = shrinker_info_srcu(memcg, nid);
        if (unlikely(!info))
                goto unlock;
 
-       for_each_set_bit(i, info->map, info->map_nr_max) {
+       generation = atomic_read(&shrinker_srcu_generation);
+       for_each_set_bit_from(i, info->map, info->map_nr_max) {
                struct shrink_control sc = {
                        .gfp_mask = gfp_mask,
                        .nid = nid,
@@ -963,6 +968,11 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
                                set_shrinker_bit(memcg, nid, i);
                }
                freed += ret;
+               if (atomic_read(&shrinker_srcu_generation) != generation) {
+                       srcu_read_unlock(&shrinker_srcu, srcu_idx);
+                       i++;
+                       goto again;
+               }
        }
 unlock:
        srcu_read_unlock(&shrinker_srcu, srcu_idx);
@@ -1002,7 +1012,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
 {
        unsigned long ret, freed = 0;
        struct shrinker *shrinker;
-       int srcu_idx;
+       int srcu_idx, generation;
 
        /*
         * The root memcg might be allocated even though memcg is disabled
@@ -1016,6 +1026,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
 
        srcu_idx = srcu_read_lock(&shrinker_srcu);
 
+       generation = atomic_read(&shrinker_srcu_generation);
        list_for_each_entry_srcu(shrinker, &shrinker_list, list,
                                 srcu_read_lock_held(&shrinker_srcu)) {
                struct shrink_control sc = {
@@ -1028,6 +1039,11 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
                if (ret == SHRINK_EMPTY)
                        ret = 0;
                freed += ret;
+
+               if (atomic_read(&shrinker_srcu_generation) != generation) {
+                       freed = freed ? : 1;
+                       break;
+               }
        }
 
        srcu_read_unlock(&shrinker_srcu, srcu_idx);