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From: Hugh Dickins <>
To: Balbir Singh <>
Cc: Pavel Emelyanov <>,
	Andrew Morton <>,
	Sudhir Kumar <>,
	YAMAMOTO Takashi <>,
	Paul Menage <>,,,,,
	David Rientjes <>,
	KAMEZAWA Hiroyuki <>
Subject: Re: [PATCH] Move memory controller allocations to their own slabs (v2)
Date: Tue, 11 Mar 2008 13:05:44 +0000 (GMT)	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Tue, 11 Mar 2008, Balbir Singh wrote:
> On my 64 bit powerpc system (structure size could be different on other systems)
> 1. sizeof page_cgroup is 40 bytes
>    which means kmalloc will allocate 64 bytes
> 2. With 4K pagesize SLAB with HWCACHE_ALIGN, 59 objects are packed per slab
> 3. With SLUB the value is 102 per slab

I expect you got those numbers with 2.6.25-rc4?  Towards the end of -rc5
there's a patch from Nick to make SLUB's treatment of HWCACHE_ALIGN the
same as SLAB's, so I expect you'd be back to a similar poor density with
SLUB too.  (But I'm replying without actually testing it out myself.)

I think you'd need a strong reason to choose HWCACHE_ALIGN for these.

Consider: the (normal configuration) x86_64 struct page size was 56
bytes for a long time (and still is without MEM_RES_CTLR), but we've
never inserted padding to make that a round 64 bytes (and they would
benefit additionally from some simpler arithmetic, not the case with
page_cgroups).  Though it's good to avoid unnecessary sharing and
multiple cacheline accesses, it's not so good as to justify almost
doubling the size of a very very common structure.  I think.


  reply	other threads:[~2008-03-12  0:04 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-03-11  6:18 Balbir Singh
2008-03-11  8:11 ` Pavel Emelyanov
2008-03-11  8:15   ` Balbir Singh
2008-03-11  8:35     ` Pavel Emelyanov
2008-03-11 11:09       ` Balbir Singh
2008-03-11 13:05         ` Hugh Dickins [this message]
2008-03-12  3:38           ` Nick Piggin
2008-03-12  3:48           ` Balbir Singh
2008-03-11 12:55 ` Hugh Dickins
2008-03-11 18:47   ` Balbir Singh

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