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Revert "mm: vmscan: add shrinker_srcu_generation"
This reverts commit475733dda5
. Kernel test robot reports -88.8% regression in stress-ng.ramfs.ops_per_sec test case [1], which is caused by commitf95bdb700b
("mm: vmscan: make global slab shrink lockless"). The root cause is that SRCU has to be careful to not frequently check for SRCU read-side critical section exits. Therefore, even if no one is currently in the SRCU read-side critical section, synchronize_srcu() cannot return quickly. That's why unregister_shrinker() has become slower. We will try to use the refcount+RCU method [2] proposed by Dave Chinner to continue to re-implement the lockless slab shrink. So revert the shrinker_srcu related changes first. [1]. https://lore.kernel.org/lkml/202305230837.db2c233f-yujie.liu@intel.com/ [2]. https://lore.kernel.org/lkml/ZIJhou1d55d4H1s0@dread.disaster.area/ Link: https://lkml.kernel.org/r/20230609081518.3039120-6-qi.zheng@linux.dev Reported-by: kernel test robot <yujie.liu@intel.com> Closes: https://lore.kernel.org/oe-lkp/202305230837.db2c233f-yujie.liu@intel.com Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Kirill Tkhai <tkhai@ya.ru> Cc: Muchun Song <muchun.song@linux.dev> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
parent
1a554ecc97
commit
d6ecbcd70f
24
mm/vmscan.c
24
mm/vmscan.c
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@ -192,7 +192,6 @@ int vm_swappiness = 60;
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LIST_HEAD(shrinker_list);
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DECLARE_RWSEM(shrinker_rwsem);
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DEFINE_SRCU(shrinker_srcu);
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static atomic_t shrinker_srcu_generation = ATOMIC_INIT(0);
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#ifdef CONFIG_MEMCG
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static int shrinker_nr_max;
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@ -818,7 +817,6 @@ void unregister_shrinker(struct shrinker *shrinker)
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debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
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up_write(&shrinker_rwsem);
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atomic_inc(&shrinker_srcu_generation);
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synchronize_srcu(&shrinker_srcu);
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shrinker_debugfs_remove(debugfs_entry, debugfs_id);
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@ -840,7 +838,6 @@ void synchronize_shrinkers(void)
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{
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down_write(&shrinker_rwsem);
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up_write(&shrinker_rwsem);
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atomic_inc(&shrinker_srcu_generation);
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synchronize_srcu(&shrinker_srcu);
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}
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EXPORT_SYMBOL(synchronize_shrinkers);
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@ -950,20 +947,18 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
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{
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struct shrinker_info *info;
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unsigned long ret, freed = 0;
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int srcu_idx, generation;
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int i = 0;
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int srcu_idx;
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int i;
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if (!mem_cgroup_online(memcg))
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return 0;
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again:
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srcu_idx = srcu_read_lock(&shrinker_srcu);
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info = shrinker_info_srcu(memcg, nid);
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if (unlikely(!info))
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goto unlock;
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generation = atomic_read(&shrinker_srcu_generation);
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for_each_set_bit_from(i, info->map, info->map_nr_max) {
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for_each_set_bit(i, info->map, info->map_nr_max) {
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struct shrink_control sc = {
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.gfp_mask = gfp_mask,
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.nid = nid,
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@ -1009,11 +1004,6 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
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set_shrinker_bit(memcg, nid, i);
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}
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freed += ret;
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if (atomic_read(&shrinker_srcu_generation) != generation) {
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srcu_read_unlock(&shrinker_srcu, srcu_idx);
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i++;
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goto again;
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}
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}
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unlock:
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srcu_read_unlock(&shrinker_srcu, srcu_idx);
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@ -1053,7 +1043,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
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{
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unsigned long ret, freed = 0;
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struct shrinker *shrinker;
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int srcu_idx, generation;
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int srcu_idx;
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/*
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* The root memcg might be allocated even though memcg is disabled
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@ -1067,7 +1057,6 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
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srcu_idx = srcu_read_lock(&shrinker_srcu);
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generation = atomic_read(&shrinker_srcu_generation);
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list_for_each_entry_srcu(shrinker, &shrinker_list, list,
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srcu_read_lock_held(&shrinker_srcu)) {
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struct shrink_control sc = {
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@ -1080,11 +1069,6 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
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if (ret == SHRINK_EMPTY)
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ret = 0;
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freed += ret;
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if (atomic_read(&shrinker_srcu_generation) != generation) {
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freed = freed ? : 1;
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break;
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}
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}
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srcu_read_unlock(&shrinker_srcu, srcu_idx);
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