linux-kernel - Re: [PATCH 1/3] mm/slub: Fix slub calculate active slabs uncorrectly

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Date:	Tue, 2 Jul 2013 14:15:42 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>
cc:	Pekka Enberg <penberg@...nel.org>, Matt Mackall <mpm@...enic.com>,
	Glauber Costa <glommer@...allels.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Joonsoo Kim <js1304@...il.com>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] mm/slub: Fix slub calculate active slabs
 uncorrectly

On Tue, 2 Jul 2013, Wanpeng Li wrote:

> Before patch:
> Active / Total Slabs (% used) : 59018 / 59018 (100.0%)
>
> After patch:
> Active / Total Slabs (% used) : 11086 / 11153 (99.4%)

Yes I saw that.

> These numbers are dump from slabtop for monitor slub, before patch Active / Total
> Slabs are always 100%, this is not truth since empty slabs present. However, the
> slab allocator can caculate its Active / Total Slabs correctly and its value is
> less than 100.0%. By comparison, slub is more efficient than slab through slabtop
> observation, however, it is not truth since slub uncorrectly calculate its
> Active / Total Slabs.

I always thought about the "empty" slabs to be active since they are used
for allocation and frees like the other partial slabs.

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