Messages in this thread | ![/](/images/icornerl.gif) | | Date | Sun, 26 Feb 2023 21:56:10 +0800 | Subject | Re: [PATCH v2 2/7] mm: vmscan: make global slab shrink lockless | From | Qi Zheng <> |
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On 2023/2/26 05:28, Kirill Tkhai wrote: > On 25.02.2023 19:37, Qi Zheng wrote: >> >> >> On 2023/2/26 00:17, Kirill Tkhai wrote: >>> On 25.02.2023 18:57, Qi Zheng wrote: >>>> >> <...> >>>> How about this? >>>>>> >>>>>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>>>>> index ffddbd204259..9d8c53075298 100644 >>>>>> --- a/mm/vmscan.c >>>>>> +++ b/mm/vmscan.c >>>>>> @@ -1012,7 +1012,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, >>>>>> int priority) >>>>>> { >>>>>> unsigned long ret, freed = 0; >>>>>> - struct shrinker *shrinker; >>>>>> + struct shrinker *shrinker = NULL; >>>>>> int srcu_idx, generation; >>>>>> >>>>>> /* >>>>>> @@ -1025,11 +1025,15 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, >>>>>> if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg)) >>>>>> return shrink_slab_memcg(gfp_mask, nid, memcg, priority); >>>>>> >>>>>> +again: >>>>>> 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)) { >>>>>> + if (!shrinker) >>>>>> + shrinker = list_entry_rcu(shrinker_list.next, struct shrinker, list); >>>>>> + else >>>>>> + shrinker = list_entry_rcu(shrinker->list.next, struct shrinker, list); >>>>>> + list_for_each_entry_from_rcu(shrinker, &shrinker_list, list) { >>>>>> struct shrink_control sc = { >>>>>> .gfp_mask = gfp_mask, >>>>>> .nid = nid, >>>>>> @@ -1042,8 +1046,9 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, >>>>>> freed += ret; >>>>>> >>>>>> if (atomic_read(&shrinker_srcu_generation) != generation) { >>>>>> - freed = freed ? : 1; >>>>>> - break; >>>>>> + srcu_read_unlock(&shrinker_srcu, srcu_idx); >>> >>> After SRCU in unlocked we can't believe @shrinker anymore. So, above list_entry_rcu(shrinker->list.next) >>> dereferences some random memory. >> >> Indeed. >> >>> >>>>>> + cond_resched(); >>>>>> + goto again; >>>>>> } >>>>>> } >>>>>> >>>>>>> >>>>>>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>>>>>> index 27ef9946ae8a..0b197bba1257 100644 >>>>>>> --- 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); >>>>>>> DEFINE_MUTEX(shrinker_mutex); >>>>>>> DEFINE_SRCU(shrinker_srcu); >>>>>>> +static atomic_t shrinker_srcu_generation = ATOMIC_INIT(0); >>>>>>> #ifdef CONFIG_MEMCG >>>>>>> static int shrinker_nr_max; >>>>>>> @@ -782,6 +783,7 @@ void unregister_shrinker(struct shrinker *shrinker) >>>>>>> debugfs_entry = shrinker_debugfs_remove(shrinker); >>>>>>> mutex_unlock(&shrinker_mutex); >>>>>>> + atomic_inc(&shrinker_srcu_generation); >>>>>>> synchronize_srcu(&shrinker_srcu); >>>>>>> debugfs_remove_recursive(debugfs_entry); >>>>>>> @@ -799,6 +801,7 @@ EXPORT_SYMBOL(unregister_shrinker); >>>>>>> */ >>>>>>> void synchronize_shrinkers(void) >>>>>>> { >>>>>>> + atomic_inc(&shrinker_srcu_generation); >>>>>>> synchronize_srcu(&shrinker_srcu); >>>>>>> } >>>>>>> EXPORT_SYMBOL(synchronize_shrinkers); >>>>>>> @@ -908,18 +911,19 @@ 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, >>>>>>> @@ -965,6 +969,11 @@ 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); >>>>>> >>>>>> Maybe we can add the following code here, so as to avoid repeating the >>>>>> current id and avoid triggering softlockup: >>>>>> >>>>>> i++; >>> >>> This is OK. >>> >>>>>> cond_resched(); >>> >>> Possible, existing cond_resched() in do_shrink_slab() is enough. >> >> Yeah. >> >> I will add this patch in the next version. May I mark you as the author >> of this patch? > > I think, yes
Thanks. :)
Qi
> >>> >>>> And this. :) >>>> >>>> Thanks, >>>> Qi >>>> >>>>>> >>>>>> Thanks, >>>>>> Qi >>>>>> >>>>>>> + goto again; >>>>>>> + } >>>>>>> } >>>>>>> unlock: >>>>>>> srcu_read_unlock(&shrinker_srcu, srcu_idx); >>>>>>> @@ -1004,7 +1013,7 @@ 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 >>>>>>> @@ -1017,6 +1026,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, >>>>>>> return shrink_slab_memcg(gfp_mask, nid, memcg, priority); >>>>>>> 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)) { >>>>>>> @@ -1030,6 +1040,11 @@ 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); >>>>>>> >>>>>>> >>>>>> >>>>> >>>> >>> >> >
-- Thanks, Qi
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