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Date: Tue, 22 Oct 2002 12:26:55 -0200 (BRST)
From: Rik van Riel <riel@conectiva.com.br>
X-X-Sender: riel@imladris.surriel.com
To: "Eric W. Biederman" <ebiederm@xmission.com>
cc: "Martin J. Bligh" <mbligh@aracnet.com>, Bill Davidsen <davidsen@tmr.com>,
       Dave McCracken <dmccr@us.ibm.com>, Andrew Morton <akpm@digeo.com>,
       Linux Kernel <linux-kernel@vger.kernel.org>,
       Linux Memory Management <linux-mm@kvack.org>
Subject: Re: [PATCH 2.5.43-mm2] New shared page table patch
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On 21 Oct 2002, Eric W. Biederman wrote:
> "Martin J. Bligh" <mbligh@aracnet.com> writes:
>
> > > So why has no one written a pte_chain reaper?  It is perfectly sane
> > > to allocate a swap entry and move an entire pte_chain to the swap
> > > cache.
> >
> > I think the underlying subsystem does not easily allow for dynamic regeneration,
> > so it's non-trivial.
>
> We swap pages out all of the time in 2.4.x, and that is all I was
> suggesting swap out some but not all of the pages, on a very long
> pte_chain.  And swapping out a page is not terribly complex, unless
> something very drastic has changed.

Imagine a slightly larger than normal Oracle server.
Say 5000 processes with 1 GB of shared memory.

Just the page tables needed to map this memory would
take up 5 GB of RAM ... with shared page tables we
only need 1 MB of page tables.

The corresponding reduction in rmaps is a nice bonus,
but hardly any more dramatic than the page table
overhead.

In short, we really really want shared page tables.

regards,

Rik
-- 
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