linux-kernel - Re: Why half of slabs are not shown in /proc/slabinfo?

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Message-ID: <Pine.LNX.4.64.0906211230590.5000@sister.anvils>
Date:	Sun, 21 Jun 2009 12:36:22 +0100 (BST)
From:	Hugh Dickins <hugh.dickins@...cali.co.uk>
To:	Andrey Borzenkov <arvidjaar@...l.ru>
cc:	linux-kernel@...r.kernel.org
Subject: Re: Why half of slabs are not shown in /proc/slabinfo?

On Sun, 21 Jun 2009, Andrey Borzenkov wrote:
> Mandriva kernel 2.6.30 using SLUB:
> 
> {pts/1}% grep SLUB /boot/config
> CONFIG_SLUB_DEBUG=y
> CONFIG_SLUB=y
> # CONFIG_SLUB_DEBUG_ON is not set
> # CONFIG_SLUB_STATS is not set
> 
> Some of slabs (e.g. filp) are not shown in /proc/slabinfo; comparing 
> number of entries under /sys and slabinfo results in
> 
> {pts/0}% =ls -1 /sys/kernel/slab | grep -v : | wc -l
> 131
> {pts/0}% wc -l /proc/slabinfo
> 68 /proc/slabinfo
> {pts/0}%
> 
> so almost half of the all entries are missing. Is it expected or there 
> is something wrong here?

With SLUB it is expected: unlike SLAB, it merges together caches
of the same size.

"slabinfo -a" (from Documentation/vm/slabinfo.c) should show you
which caches have got aliased together.

It can be quite tiresome if you're doing an investigation:
booting with "slub_nomerge" stops it behaving like that.

Hugh
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