linux-kernel - Re: [PATCH 1/2] zsmalloc: do not scan for allocated objects in empty zspage

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Message-ID: <20230623104917.2n6vcxvhvlwmjm2m@cab-wsm-0029881>
Date:   Fri, 23 Jun 2023 10:49:07 +0000
From:   Alexey Romanov <AVRomanov@...rdevices.ru>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
CC:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] zsmalloc: do not scan for allocated objects in empty
 zspage

Hello!

On Fri, Jun 23, 2023 at 01:40:01PM +0900, Sergey Senozhatsky wrote:
> zspage migration can terminate as soon as it moves the last
> allocated object from the source zspage.  Add a simple helper
> zspage_empty() that tests zspage ->inuse on each migration
> iteration.
> 
> Suggested-by: Alexey Romanov <AVRomanov@...rdevices.ru>
> Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> ---
>  mm/zsmalloc.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 3f057970504e..5d60eaedc3b7 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1147,6 +1147,11 @@ static bool zspage_full(struct size_class *class, struct zspage *zspage)
>  	return get_zspage_inuse(zspage) == class->objs_per_zspage;
>  }
>  
> +static bool zspage_empty(struct zspage *zspage)
> +{
> +	return get_zspage_inuse(zspage) == 0;
> +}
> +
>  /**
>   * zs_lookup_class_index() - Returns index of the zsmalloc &size_class
>   * that hold objects of the provided size.
> @@ -1625,6 +1630,10 @@ static void migrate_zspage(struct zs_pool *pool, struct size_class *class,
>  		obj_idx++;
>  		record_obj(handle, free_obj);
>  		obj_free(class->size, used_obj);
> +
> +		/* Stop if there are no more objects to migrate */
> +		if (zspage_empty(get_zspage(s_page)))
> +			break;
>  	}
>  
>  	/* Remember last position in this iteration */
> -- 
> 2.41.0.162.gfafddb0af9-goog
> 

I think we can add similar check in zs_reclaim_page() function.
There we also scan zspage to find the allocated object.

-- 
Thank you,
Alexey