Re: [PATCH v2 1/7] mm: vmscan: add a map_nr_max field to shrinker_info
From: Kirill Tkhai
Date: Sat Feb 25 2023 - 10:14:58 EST
Hi Qi,
On 25.02.2023 11:18, Qi Zheng wrote:
>
>
> On 2023/2/23 21:27, Qi Zheng wrote:
>> To prepare for the subsequent lockless memcg slab shrink,
>> add a map_nr_max field to struct shrinker_info to records
>> its own real shrinker_nr_max.
>>
>> No functional changes.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
>
> I missed Suggested-by here, hi Kirill, can I add it?
>
> Suggested-by: Kirill Tkhai <tkhai@xxxxx>
Yes, feel free to add this tag.
There is a comment below.
>> ---
>> include/linux/memcontrol.h | 1 +
>> mm/vmscan.c | 29 ++++++++++++++++++-----------
>> 2 files changed, 19 insertions(+), 11 deletions(-)
>>
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index b6eda2ab205d..aa69ea98e2d8 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -97,6 +97,7 @@ struct shrinker_info {
>> struct rcu_head rcu;
>> atomic_long_t *nr_deferred;
>> unsigned long *map;
>> + int map_nr_max;
>> };
>> struct lruvec_stats_percpu {
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 9c1c5e8b24b8..9f895ca6216c 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -224,9 +224,16 @@ static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
>> lockdep_is_held(&shrinker_rwsem));
>> }
>> +static inline bool need_expand(int new_nr_max, int old_nr_max)
>> +{
>> + return round_up(new_nr_max, BITS_PER_LONG) >
>> + round_up(old_nr_max, BITS_PER_LONG);
>> +}
>> +
>> static int expand_one_shrinker_info(struct mem_cgroup *memcg,
>> int map_size, int defer_size,
>> - int old_map_size, int old_defer_size)
>> + int old_map_size, int old_defer_size,
>> + int new_nr_max)
>> {
>> struct shrinker_info *new, *old;
>> struct mem_cgroup_per_node *pn;
>> @@ -240,12 +247,16 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
>> if (!old)
>> return 0;
>> + if (!need_expand(new_nr_max, old->map_nr_max))
>> + return 0;
>> +
>> new = kvmalloc_node(sizeof(*new) + size, GFP_KERNEL, nid);
>> if (!new)
>> return -ENOMEM;
>> new->nr_deferred = (atomic_long_t *)(new + 1);
>> new->map = (void *)new->nr_deferred + defer_size;
>> + new->map_nr_max = new_nr_max;
>> /* map: set all old bits, clear all new bits */
>> memset(new->map, (int)0xff, old_map_size);
>> @@ -295,6 +306,7 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
>> }
>> info->nr_deferred = (atomic_long_t *)(info + 1);
>> info->map = (void *)info->nr_deferred + defer_size;
>> + info->map_nr_max = shrinker_nr_max;
>> rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
>> }
>> up_write(&shrinker_rwsem);
>> @@ -302,12 +314,6 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
>> return ret;
>> }
>> -static inline bool need_expand(int nr_max)
>> -{
>> - return round_up(nr_max, BITS_PER_LONG) >
>> - round_up(shrinker_nr_max, BITS_PER_LONG);
>> -}
>> -
>> static int expand_shrinker_info(int new_id)
>> {
>> int ret = 0;
>> @@ -316,7 +322,7 @@ static int expand_shrinker_info(int new_id)
>> int old_map_size, old_defer_size = 0;
>> struct mem_cgroup *memcg;
>> - if (!need_expand(new_nr_max))
>> + if (!need_expand(new_nr_max, shrinker_nr_max))
>> goto out;
>> if (!root_mem_cgroup)
>> @@ -332,7 +338,8 @@ static int expand_shrinker_info(int new_id)
>> memcg = mem_cgroup_iter(NULL, NULL, NULL);
>> do {
>> ret = expand_one_shrinker_info(memcg, map_size, defer_size,
>> - old_map_size, old_defer_size);
>> + old_map_size, old_defer_size,
>> + new_nr_max);
>> if (ret) {
>> mem_cgroup_iter_break(NULL, memcg);
>> goto out;
>> @@ -432,7 +439,7 @@ void reparent_shrinker_deferred(struct mem_cgroup *memcg)
>> for_each_node(nid) {
>> child_info = shrinker_info_protected(memcg, nid);
>> parent_info = shrinker_info_protected(parent, nid);
>> - for (i = 0; i < shrinker_nr_max; i++) {
>> + for (i = 0; i < child_info->map_nr_max; i++) {
>> nr = atomic_long_read(&child_info->nr_deferred[i]);
>> atomic_long_add(nr, &parent_info->nr_deferred[i]);
>> }
>> @@ -899,7 +906,7 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
>> if (unlikely(!info))
>> goto unlock;
>> - for_each_set_bit(i, info->map, shrinker_nr_max) {
>> + for_each_set_bit(i, info->map, info->map_nr_max) {
>> struct shrink_control sc = {
>> .gfp_mask = gfp_mask,
>> .nid = nid,
The patch as whole thing won't work as expected. It won't ever call shrinker with ids from [round_down(shrinker_nr_max, sizeof(unsigned long)) + 1, shrinker_nr_max - 1]
Just replay the sequence we add new shrinkers:
1)We add shrinker #0:
shrinker_nr_max = 0;
prealloc_memcg_shrinker()
id = 0;
expand_shrinker_info(0)
new_nr_max = 1;
expand_one_shrinker_info(new_nr_max = 1)
new->map_nr_max = 1;
shrinker_nr_max = 1;
2)We add shrinker #1:
prealloc_memcg_shrinker()
id = 1;
expand_shrinker_info(1)
new_nr_max = 2;
need_expand(2, 1) => false => ignore expand
shrinker_nr_max = 2;
3)Then we call shrinker:
shrink_slab_memcg()
for_each_set_bit(i, info->map, 1/* info->map_nr_max */ ) {
} => ignore shrinker #1
I'd fixed this patch by something like the below:
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9f895ca6216c..bb617a3871f1 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -224,12 +224,6 @@ static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
lockdep_is_held(&shrinker_rwsem));
}
-static inline bool need_expand(int new_nr_max, int old_nr_max)
-{
- return round_up(new_nr_max, BITS_PER_LONG) >
- round_up(old_nr_max, BITS_PER_LONG);
-}
-
static int expand_one_shrinker_info(struct mem_cgroup *memcg,
int map_size, int defer_size,
int old_map_size, int old_defer_size,
@@ -247,9 +241,6 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg,
if (!old)
return 0;
- if (!need_expand(new_nr_max, old->map_nr_max))
- return 0;
-
new = kvmalloc_node(sizeof(*new) + size, GFP_KERNEL, nid);
if (!new)
return -ENOMEM;
@@ -317,14 +308,11 @@ int alloc_shrinker_info(struct mem_cgroup *memcg)
static int expand_shrinker_info(int new_id)
{
int ret = 0;
- int new_nr_max = new_id + 1;
+ int new_nr_max = round_up(new_id + 1, BITS_PER_LONG);
int map_size, defer_size = 0;
int old_map_size, old_defer_size = 0;
struct mem_cgroup *memcg;
- if (!need_expand(new_nr_max, shrinker_nr_max))
- goto out;
-
if (!root_mem_cgroup)
goto out;
@@ -359,9 +347,11 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
rcu_read_lock();
info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
- /* Pairs with smp mb in shrink_slab() */
- smp_mb__before_atomic();
- set_bit(shrinker_id, info->map);
+ if (!WARN_ON_ONCE(shrinker_id >= info->map_nr_max)) {
+ /* Pairs with smp mb in shrink_slab() */
+ smp_mb__before_atomic();
+ set_bit(shrinker_id, info->map);
+ }
rcu_read_unlock();
}
}
(I also added a new check into set_shrinker_bit() for safety).
Kirill