On 22.01.2021 02:06, Yang Shi wrote:
> Both memcg_shrinker_map_size and shrinker_nr_max is maintained, but actually the
> map size can be calculated via shrinker_nr_max, so it seems unnecessary to keep both.
> Remove memcg_shrinker_map_size since shrinker_nr_max is also used by iterating the
> bit map.
>
> Signed-off-by: Yang Shi <shy828301@xxxxxxxxx>
> ---
> mm/vmscan.c | 16 +++++++---------
> 1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index d3f3701dfcd2..40e7751ef961 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -185,8 +185,7 @@ static LIST_HEAD(shrinker_list);
> static DECLARE_RWSEM(shrinker_rwsem);
>
> #ifdef CONFIG_MEMCG
> -
> -static int memcg_shrinker_map_size;
> +static int shrinker_nr_max;
>
> static void free_shrinker_map_rcu(struct rcu_head *head)
> {
> @@ -248,7 +247,7 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
> return 0;
>
> down_write(&shrinker_rwsem);
> - size = memcg_shrinker_map_size;
> + size = (shrinker_nr_max / BITS_PER_LONG + 1) * sizeof(unsigned long);
> for_each_node(nid) {
> map = kvzalloc_node(sizeof(*map) + size, GFP_KERNEL, nid);
> if (!map) {
> @@ -266,10 +265,11 @@ int alloc_shrinker_maps(struct mem_cgroup *memcg)
> static int expand_shrinker_maps(int new_id)
> {
> int size, old_size, ret = 0;
> + int new_nr_max = new_id + 1;
> struct mem_cgroup *memcg;
>
> - size = DIV_ROUND_UP(new_id + 1, BITS_PER_LONG) * sizeof(unsigned long);
> - old_size = memcg_shrinker_map_size;
> + size = (new_nr_max / BITS_PER_LONG + 1) * sizeof(unsigned long);
> + old_size = (shrinker_nr_max / BITS_PER_LONG + 1) * sizeof(unsigned long);
>
> if (size <= old_size)
> return 0;
This looks a BUG:
expand_shrinker_maps(id == 1)
{
old_size = 64;
size = 64;
===>return 0 and shrinker_nr_max remains 0.
}
Then shrink_slab_memcg() misses this shrinker since shrinker_nr_max == 0.
>
> @@ -286,9 +286,10 @@ static int expand_shrinker_maps(int new_id)
> goto out;
> }
> } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
> +
> out:
> if (!ret)
> - memcg_shrinker_map_size = size;
> + shrinker_nr_max = new_nr_max;
>
> return ret;
> }
> @@ -321,7 +322,6 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
> #define SHRINKER_REGISTERING ((struct shrinker *)~0UL)
>
> static DEFINE_IDR(shrinker_idr);
> -static int shrinker_nr_max;
>
> static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> {
> @@ -338,8 +338,6 @@ static int prealloc_memcg_shrinker(struct shrinker *shrinker)
> idr_remove(&shrinker_idr, id);
> goto unlock;
> }
> -
> - shrinker_nr_max = id + 1;
> }
> shrinker->id = id;
> ret = 0;
>
