[Devel] [PATCH rh7 v4] mm/memcg: fix cache growth above cache.limit_in_bytes

[Evgenii Shatokhin]

Hi,

On 30.07.2020 18:02, Andrey Ryabinin wrote:
> Exceeding cache above cache.limit_in_bytes schedules high_work_func()
> which tries to reclaim 32 pages. If cache generated fast enough or it allows
> cgroup to steadily grow above cache.limit_in_bytes because we don't reclaim
> enough. Try to reclaim exceeded amount of cache instead.
> 
> https://jira.sw.ru/browse/PSBM-106384
> Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
> ---
> 
>   - Changes since v1: add bug link to changelog
>   - Changes since v2: Fix cache_overused check (We should check if it's positive).
>      Made this stupid bug during cleanup, patch was tested without bogus cleanup,
>      so it shoud work.
>   - Chnages since v3: Compilation fixes, properly tested now.
> 
>   mm/memcontrol.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 3cf200f506c3..16cbd451a588 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3080,12 +3080,16 @@ static void reclaim_high(struct mem_cgroup *memcg,
>   {
>   
>   	do {
> +		long cache_overused;
> +
>   		if (page_counter_read(&memcg->memory) > memcg->high)
>   			try_to_free_mem_cgroup_pages(memcg, nr_pages, gfp_mask, 0);
>   
> -		if (page_counter_read(&memcg->cache) > memcg->cache.limit)
> -			try_to_free_mem_cgroup_pages(memcg, nr_pages, gfp_mask,
> -						MEM_CGROUP_RECLAIM_NOSWAP);
> +		cache_overused = page_counter_read(&memcg->cache) -
> +			memcg->cache.limit;

If cache_overused is less than 32 pages, the kernel would try to reclaim 
less than before the patch. It it OK, or should it try to reclaim at 
least 32 pages?

> +		if (cache_overused > 0)
> +			try_to_free_mem_cgroup_pages(memcg, cache_overused,
> +					gfp_mask, MEM_CGROUP_RECLAIM_NOSWAP);
>   
>   	} while ((memcg = parent_mem_cgroup(memcg)));
>   }
>