linux-kernel - Re: [RFC v2 PATCH] mm, sl[au]b: Introduce lockless cache

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Message-ID: <20210922091153.GA80396@kvm.asia-northeast3-a.c.our-ratio-313919.internal>
Date:   Wed, 22 Sep 2021 09:11:53 +0000
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-mm@...ck.org, Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>,
        John Garry <john.garry@...wei.com>,
        linux-block@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [RFC v2 PATCH] mm, sl[au]b: Introduce lockless cache

> @@ -491,13 +492,13 @@ void kmem_cache_free_cached(struct kmem_cache *s, void *p)
>         cache = get_cpu_ptr(s->cache);
>         if (cache->size < KMEM_LOCKLESS_CACHE_QUEUE_SIZE) {
>                 cache->queue[cache->size++] = p;
> -               put_cpu_ptr(s->cache);
> -               return ;
> +       } else {
> +               kmem_cache_free_bulk(s,
> +                               KMEM_LOCKLESS_CACHE_BATCHCOUNT,
> +                               cache->queue - KMEM_LOCKLESS_CACHE_BATCHCOUNT);
> +               cache->size -= KMEM_LOCKLESS_CACHE_BATCHCOUNT;
>         }
>         put_cpu_ptr(s->cache);
> -
> -       /* Is there better way to do this? */
> -       kmem_cache_free(s, p);
>  }
>  EXPORT_SYMBOL(kmem_cache_free_cached);

Sent you a wrong code.

Above was buggy code from some hours ago 
because of cache->queue - KMEM_LOCKLESS_CACHE_BATCHCOUNT.

So that is now:

	cache = get_cpu_ptr(s->cache);
	if (cache->size < KMEM_LOCKLESS_CACHE_QUEUE_SIZE) {
		cache->queue[cache->size++] = p;
	} else {
		kmem_cache_free_bulk(s,
				KMEM_LOCKLESS_CACHE_BATCHCOUNT,
				cache->queue + KMEM_LOCKLESS_CACHE_QUEUE_SIZE
				- KMEM_LOCKLESS_CACHE_BATCHCOUNT);
		cache->size -= KMEM_LOCKLESS_CACHE_BATCHCOUNT;
	}
	put_cpu_ptr(s->cache);