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Date:   Tue, 7 Jul 2020 06:59:04 +0000 (UTC)
From:   Christopher Lameter <cl@linux.com>
To:     Xunlei Pang <xlpang@linux.alibaba.com>
cc:     Andrew Morton <akpm@linux-foundation.org>,
        Wen Yang <wenyang@linux.alibaba.com>,
        Yang Shi <yang.shi@linux.alibaba.com>,
        Roman Gushchin <guro@fb.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] mm/slub: Introduce two counters for the partial
 objects
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On Thu, 2 Jul 2020, Xunlei Pang wrote:

> This patch introduces two counters to maintain the actual number
> of partial objects dynamically instead of iterating the partial
> page lists with list_lock held.
>
> New counters of kmem_cache_node are: pfree_objects, ptotal_objects.
> The main operations are under list_lock in slow path, its performance
> impact is minimal.


If at all then these counters need to be under CONFIG_SLUB_DEBUG.

> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -616,6 +616,8 @@ struct kmem_cache_node {
>  #ifdef CONFIG_SLUB
>  	unsigned long nr_partial;
>  	struct list_head partial;
> +	atomic_long_t pfree_objects; /* partial free objects */
> +	atomic_long_t ptotal_objects; /* partial total objects */

Please in the CONFIG_SLUB_DEBUG. Without CONFIG_SLUB_DEBUG we need to
build with minimal memory footprint.

>  #ifdef CONFIG_SLUB_DEBUG
>  	atomic_long_t nr_slabs;
>  	atomic_long_t total_objects;
> diff --git a/mm/slub.c b/mm/slub.c


Also this looks to be quite heavy on the cache and on execution time. Note
that the list_lock could be taken frequently in the performance sensitive
case of freeing an object that is not in the partial lists.