linux-kernel - Re: [PATCH] mm: zram: amend SLAB_RECLAIM_ACCOUNT on zspage

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Date:   Fri, 18 Jun 2021 15:02:47 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Huangzhaoyang <huangzhaoyang@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Nitin Gupta <ngupta@...are.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH] mm: zram: amend SLAB_RECLAIM_ACCOUNT on zspage_cachep

On Tue, Jun 08, 2021 at 03:28:17PM +0800, Huangzhaoyang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> 
> Zspage_cachep is found be merged with other kmem cache during test, which
> is not good for debug things(zs_pool->zspage_cachep present to be another
> kmem cache in memory dumpfile). It is also neccessary to do so as shrinker has

It's not a only problem of zsmalloc because slab want to minimize
fragmentation so try to merge several objects if it's allowed.
So I don't think it's particular problem of zsmalloc.
I guess slub has some option maybe "nomerge" if you want it.

> been registered for zspage. Amending this flag can help kernel to calculate
> SLAB_RECLAIMBLE correctly.
> 
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> ---
>  mm/zsmalloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 19b563b..0b0addd 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -328,7 +328,7 @@ static int create_cache(struct zs_pool *pool)
>  		return 1;
>  
>  	pool->zspage_cachep = kmem_cache_create("zspage", sizeof(struct zspage),
> -					0, 0, NULL);
> +					0, SLAB_RECLAIM_ACCOUNT, NULL);

How does zspage become SLAB_RECLAIM_ACCOUNT?

I took the flag as "cacheable" object. IOW, when the shrinker
ask to reclaim the object, it should reclaim(e.g., discarding)
those objects for reclaming. However, that's not the case
in zsmalloc.