Re: [PATCH] mm/vmscan: add pgstall to memcg

[Andrew Morton <akpm@linux-foundation.org>]

(cc memcg developers)
On Thu, 23 Jun 2022 16:01:03 +0800 zhouchuyi <zhouchuyi@bytedance.com> wrote:

> Add pgstall to indicate the times of entering direct reclaim of memcg, use
> the item of ALLOCSTALL_NORMAL in vmevents to save the data.
> 
> Signed-off-by: zhouchuyi <zhouchuyi@bytedance.com>
> ---
> 
> 
> Hi，
> 
> I notice memcg uses some items to indicate the situation of direct reclaim in memory.stat，such as pgsteal and pgscan. 
> I think there is no harm in adding another item to show the times of entering direct reclaim.
> 

Why do you consider this useful?  Do you have a use case?  If so,
please describe it in detail.

>
> ...
>
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 176298f2f..44c5b15bd 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1447,8 +1447,11 @@ PAGE_SIZE multiple when read back.
>  
>  	  pgsteal (npn)
>  		Amount of reclaimed pages
> -
> -	  pgactivate (npn)
> +          
> +          pgstall (npn)
> +	  	Number of entering direct reclaim
> +	  
> +          pgactivate (npn)
>  		Amount of pages moved to the active LRU list
>  
>  	  pgdeactivate (npn)
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index abec50f31..f407084b2 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1505,6 +1505,8 @@ static char *memory_stat_format(struct mem_cgroup *memcg)
>  	seq_buf_printf(&s, "pgscan %lu\n",
>  		       memcg_events(memcg, PGSCAN_KSWAPD) +
>  		       memcg_events(memcg, PGSCAN_DIRECT));
> +	seq_buf_printf(&s, "pgstall %lu\n", 
> +			   memcg_events(memcg, ALLOCSTALL_NORMAL));
>  	seq_buf_printf(&s, "pgsteal %lu\n",
>  		       memcg_events(memcg, PGSTEAL_KSWAPD) +
>  		       memcg_events(memcg, PGSTEAL_DIRECT));
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index f7d9a683e..107cec59a 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -3532,7 +3532,10 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
>  
>  	if (!cgroup_reclaim(sc))
>  		__count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1);
> -
> +	else {
> +		count_memcg_events(sc->target_mem_cgroup, 
> +					ALLOCSTALL_NORMAL, 1);
> +	}
>  	do {
>  		vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
>  				sc->priority);
> -- 
> 2.20.1