linux-kernel - Re: [PATCH 2/5] zsmalloc: Consolidate zs_pool's migrate_lock and size

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Message-ID: <Y2Hj+H4VzlN/fcmR@google.com>
Date:   Wed, 2 Nov 2022 12:28:56 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Nhat Pham <nphamcs@...il.com>
Cc:     akpm@...ux-foundation.org, hannes@...xchg.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, minchan@...nel.org,
        ngupta@...are.org, senozhatsky@...omium.org, sjenning@...hat.com,
        ddstreet@...e.org, vitaly.wool@...sulko.com
Subject: Re: [PATCH 2/5] zsmalloc: Consolidate zs_pool's migrate_lock and
 size_class's locks

On (22/10/26 13:06), Nhat Pham wrote:
>  struct size_class {
> -	spinlock_t lock;
>  	struct list_head fullness_list[NR_ZS_FULLNESS];
>  	/*
>  	 * Size of objects stored in this class. Must be multiple
> @@ -247,8 +245,7 @@ struct zs_pool {
>  #ifdef CONFIG_COMPACTION
>  	struct work_struct free_work;
>  #endif
> -	/* protect page/zspage migration */
> -	rwlock_t migrate_lock;
> +	spinlock_t lock;
>  };

I'm not in love with this, to be honest. One big pool lock instead
of 255 per-class locks doesn't look attractive, as one big pool lock
is going to be hammered quite a lot when zram is used, e.g. as a regular
block device with a file system and is under heavy parallel writes/reads.