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Date: Tue, 20 Feb 2024 13:48:25 +0900
From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: Chengming Zhou <zhouchengming@bytedance.com>
Cc: nphamcs@gmail.com, yosryahmed@google.com,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	Minchan Kim <minchan@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>, hannes@cmpxchg.org,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] mm/zsmalloc: remove migrate_write_lock_nested()
Message-ID: <20240220044825.GD11472@google.com>
References: <20240219-b4-szmalloc-migrate-v1-0-34cd49c6545b@bytedance.com>
 <20240219-b4-szmalloc-migrate-v1-2-34cd49c6545b@bytedance.com>
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In-Reply-To: <20240219-b4-szmalloc-migrate-v1-2-34cd49c6545b@bytedance.com>

On (24/02/19 13:33), Chengming Zhou wrote:
>  static void migrate_write_unlock(struct zspage *zspage)
>  {
>  	write_unlock(&zspage->lock);
> @@ -2003,19 +1997,17 @@ static unsigned long __zs_compact(struct zs_pool *pool,
>  			dst_zspage = isolate_dst_zspage(class);
>  			if (!dst_zspage)
>  				break;
> -			migrate_write_lock(dst_zspage);
>  		}
>  
>  		src_zspage = isolate_src_zspage(class);
>  		if (!src_zspage)
>  			break;
>  
> -		migrate_write_lock_nested(src_zspage);
> -
> +		migrate_write_lock(src_zspage);
>  		migrate_zspage(pool, src_zspage, dst_zspage);
> -		fg = putback_zspage(class, src_zspage);
>  		migrate_write_unlock(src_zspage);
>  
> +		fg = putback_zspage(class, src_zspage);

Hmm. Lockless putback doesn't look right to me. We modify critical
zspage fileds in putback_zspage().

>  		if (fg == ZS_INUSE_RATIO_0) {
>  			free_zspage(pool, class, src_zspage);
>  			pages_freed += class->pages_per_zspage;
> @@ -2025,7 +2017,6 @@ static unsigned long __zs_compact(struct zs_pool *pool,
>  		if (get_fullness_group(class, dst_zspage) == ZS_INUSE_RATIO_100
>  		    || spin_is_contended(&pool->lock)) {
>  			putback_zspage(class, dst_zspage);
> -			migrate_write_unlock(dst_zspage);
>  			dst_zspage = NULL;
>  
>  			spin_unlock(&pool->lock);
> @@ -2034,15 +2025,12 @@ static unsigned long __zs_compact(struct zs_pool *pool,
>  		}
>  	}
>  
> -	if (src_zspage) {
> +	if (src_zspage)
>  		putback_zspage(class, src_zspage);
> -		migrate_write_unlock(src_zspage);
> -	}
>  
> -	if (dst_zspage) {
> +	if (dst_zspage)
>  		putback_zspage(class, dst_zspage);
> -		migrate_write_unlock(dst_zspage);
> -	}