From: xunlei <xlpang@linux.alibaba.com>
To: Christopher Lameter <cl@linux.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
Date: Fri, 31 Jul 2020 10:52:14 +0800 [thread overview]
Message-ID: <cf0fa2f4-86c3-655b-3a54-353bf8c1635b@linux.alibaba.com> (raw)
In-Reply-To: <alpine.DEB.2.22.394.2007070656120.1587@www.lameter.com>
On 2020/7/7 下午2:59, Christopher Lameter wrote:
> 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.
Thanks for the comments.
show_slab_objects() also calls it with CONFIG_SYSFS:
if (flags & SO_PARTIAL) {
struct kmem_cache_node *n;
for_each_kmem_cache_node(s, node, n) {
if (flags & SO_TOTAL)
x = count_partial(n, count_total);
else if (flags & SO_OBJECTS)
x = count_partial(n, count_inuse);
else
x = n->nr_partial;
total += x;
nodes[node] += x;
}
}
I'm not sure if it's due to some historical reason, it works without
CONFIG_SLUB_DEBUG.
>
>> #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.
>
Yes, the concurrent __slab_free() has potential lock/atomic contention,
how about using percpu variable for partial free like below?
static inline void
__update_partial_free(struct kmem_cache_node *n, long delta)
{
atomic_long_add(delta, this_cpu_ptr(n->partial_free_objs));
}
-Xunlei
next prev parent reply other threads:[~2020-07-31 2:52 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-02 8:32 [PATCH 1/2] mm/slub: Introduce two counters for the partial objects Xunlei Pang
2020-07-02 8:32 ` [PATCH 2/2] mm/slub: Get rid of count_partial() Xunlei Pang
2020-07-02 11:59 ` [PATCH 1/2] mm/slub: Introduce two counters for the partial objects Pekka Enberg
2020-07-03 9:37 ` xunlei
2020-07-07 15:23 ` Pekka Enberg
2020-07-09 14:32 ` Christopher Lameter
2020-07-31 2:57 ` xunlei
2020-07-07 6:59 ` Christopher Lameter
2020-07-31 2:52 ` xunlei [this message]
2020-08-06 12:42 ` Vlastimil Babka
2020-08-07 7:25 ` Pekka Enberg
2020-08-07 13:02 ` Christopher Lameter
2020-08-07 17:28 ` Pekka Enberg
2020-08-10 11:56 ` xunlei
2020-08-11 12:52 ` Christopher Lameter
2020-08-20 13:58 ` Pekka Enberg
2020-08-24 9:59 ` xunlei
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