Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:5 as permitted sender) client-ip=2620:137:e000::3:5;
Message-ID: <6257318a-3d39-ccdf-a85f-dc1008a8f425@suse.cz>
Date:   Tue, 31 Oct 2023 10:50:17 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.15.1
Subject: Re: [RFC PATCH v3 6/7] slub: Delay freezing of partial slabs
Content-Language: en-US
To:     chengming.zhou@linux.dev, cl@linux.com, penberg@kernel.org
Cc:     rientjes@google.com, iamjoonsoo.kim@lge.com,
        akpm@linux-foundation.org, roman.gushchin@linux.dev,
        42.hyeyoo@gmail.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Chengming Zhou <zhouchengming@bytedance.com>
References: <20231024093345.3676493-1-chengming.zhou@linux.dev>
 <20231024093345.3676493-7-chengming.zhou@linux.dev>
From:   Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <20231024093345.3676493-7-chengming.zhou@linux.dev>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 10/24/23 11:33, chengming.zhou@linux.dev wrote:
> From: Chengming Zhou <zhouchengming@bytedance.com>
> 
> Now we will freeze slabs when moving them out of node partial list to
> cpu partial list, this method needs two cmpxchg_double operations:
> 
> 1. freeze slab (acquire_slab()) under the node list_lock
> 2. get_freelist() when pick used in ___slab_alloc()
> 
> Actually we don't need to freeze when moving slabs out of node partial
> list, we can delay freezing to when use slab freelist in ___slab_alloc(),
> so we can save one cmpxchg_double().
> 
> And there are other good points:
>  - The moving of slabs between node partial list and cpu partial list
>    becomes simpler, since we don't need to freeze or unfreeze at all.
> 
>  - The node list_lock contention would be less, since we don't need to
>    freeze any slab under the node list_lock.
> 
> We can achieve this because there is no concurrent path would manipulate
> the partial slab list except the __slab_free() path, which is serialized
> now.

"which is now serialized by slab_test_node_partial() under the list_lock." ?

> Since the slab returned by get_partial() interfaces is not frozen anymore
> and no freelist in the partial_context, so we need to use the introduced

		 ^ is returned in

> freeze_slab() to freeze it and get its freelist.
> 
> Similarly, the slabs on the CPU partial list are not frozen anymore,
> we need to freeze_slab() on it before use.

We can now delete acquire_slab() as it became unused.

> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>

With the fixup for CONFIG_SLUB_CPU_PARTIAL you mentioned,
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>

Also agreed with followup patch to rename unfreeze_partials().
Thanks!