linux-kernel - Re: [PATCH v2 3/5] slab: restrict the number of objects in a slab

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Message-ID: <00000141d70e0e22-bd66f3af-822a-47dd-bbd9-fe68ad8da2ff-000000@email.amazonses.com>
Date:	Sun, 20 Oct 2013 18:08:44 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	JoonSoo Kim <js1304@...il.com>
cc:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Pekka Enberg <penberg@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 3/5] slab: restrict the number of objects in a slab

On Sat, 19 Oct 2013, JoonSoo Kim wrote:

> > Ok so that results in a mininum size object size of 2^(12 - 8) = 2^4 ==
> > 16 bytes on x86. This is not true for order 1 pages (which SLAB also
> > supports) where we need 32 bytes.
>
> According to current slab size calculating logic, slab whose object size is
> less or equal to 16 bytes use only order 0 page. So there is no problem.

Ok then lets add a VM_BUG_ON to detect the situation when someone tries
something different.

> > Problems may arise on PPC or IA64 where the page size may be larger than
> > 64K. With 64K we have a mininum size of 2^(16 - 8) = 256 bytes. For those
> > arches we may need 16 bit sized indexes. Maybe make that compile time
> > determined base on page size? > 64KByte results in 16 bit sized indexes?
>
> Okay. I will try it.

Again compile time. You had runtime in some earlier patches which adds new
branches to key functions.

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