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

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Date:   Wed, 2 Nov 2022 14:36:35 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Nhat Pham <nphamcs@...il.com>, akpm@...ux-foundation.org,
        hannes@...xchg.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, ngupta@...are.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 Wed, Nov 02, 2022 at 12:28:56PM +0900, Sergey Senozhatsky wrote:
> 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.
> 
I agree with Sergey.

I am also worry about that LRU stuff should be part of allocator
instead of higher level.