From: "Martin J. Bligh" <mbligh@aracnet.com>
To: Arjan van de Ven <arjan@infradead.org>, Andrew Morton <akpm@osdl.org>
Cc: Christoph Lameter <clameter@sgi.com>,
linux-kernel@vger.kernel.org, linux-mm@vger.kernel.org,
torvalds@osdl.org
Subject: Re: [PATCH] Prefaulting
Date: Mon, 14 Mar 2005 10:42:59 -0800 [thread overview]
Message-ID: <547140000.1110825779@flay> (raw)
In-Reply-To: <1110618637.6292.36.camel@laptopd505.fenrus.org>
--On Saturday, March 12, 2005 10:10:36 +0100 Arjan van de Ven <arjan@infradead.org> wrote:
>
>> > From a quick peek it seems that the patch makes negligible difference for a
>> kernel compilation when prefaulting 1-2 pages and slows the workload down
>> quite a lot when prefaulting up to 16 pages.
>
> well the last time I saw prefaulting experiments (Ingo was involved
> iirc) the problem was that the hitrate for the prefaults was such that
> the costs for tearing down the extra redundant rmap chains was more
> expensive than taking the "extra" faults. It seems linux has pretty
> cheap faulting logic invalidating some of traditional OS assumptions...
Yes - is pretty much exactly what I saw with this too, even if we only
prefaulted up to 4 pages that were already in the pagecache. The additional
cost in zap_pte_rage etc killed us, and it was wholly detrimental.
I think we need better locality in glibc, etc before this is of much use.
I had a debug patch somewhere to show how sparse the layout of ptes was,
I'll see if I can find it.
M.
prev parent reply other threads:[~2005-03-14 18:46 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-03-11 12:47 [PATCH] Prefaulting Christoph Lameter
2005-03-12 1:22 ` Andrew Morton
2005-03-12 3:30 ` Christoph Lameter
2005-03-12 3:43 ` Andrew Morton
2005-03-16 19:30 ` Christoph Lameter
2005-03-12 9:10 ` Arjan van de Ven
2005-03-14 18:42 ` Martin J. Bligh [this message]
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