linux-kernel - Re: Linux 3.19-rc3

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Message-ID: <54B491F8.1070909@redhat.com>
Date:	Mon, 12 Jan 2015 22:33:12 -0500
From:	Rik van Riel <riel@...hat.com>
To:	David Lang <david@...g.hm>,
	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Catalin Marinas <catalin.marinas@....com>,
	Mark Langsdorf <mlangsdo@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: Linux 3.19-rc3

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On 01/09/2015 09:51 PM, David Lang wrote:
> On Fri, 9 Jan 2015, Linus Torvalds wrote:
> 
>> Big pages are a bad bad bad idea. They work fine for databases,
>> and that's pretty much just about it. I'm sure there are some
>> other loads, but they are few and far between.
> 
> what about a dedicated virtualization host (where your workload is
> a handful of virtual machines), would the file cache issue still
> be overwelming, even though it's the virtual machines accessing
> things?

You would still have page cache inside the guest.

Using large pages in the host, and small pages in the guest
would not give you the TLB benefits, and that is assuming
that different page sizes in host and guest even work...

Using large pages in the guests gets you back to the wasted
memory, except you are now wasting memory in a situation where
you have less memory available in each guest. Density is a real
consideration for virtualization.

- -- 
All rights reversed
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