From: Avi Kivity <avi@redhat.com>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: "peter.lieven@gmail.com" <pl@dlh.net>,
qemu-devel@nongnu.org, kvm@vger.kernel.org
Subject: Re: [Qemu-devel] linux guests and ksm performance
Date: Tue, 28 Feb 2012 15:16:31 +0200 [thread overview]
Message-ID: <4F4CD3AF.7090709@redhat.com> (raw)
In-Reply-To: <CAJSP0QUfBqso18ZSS9htbKQ4WxLj1+fcB0nMNXP_4sGdwUeD8Q@mail.gmail.com>
On 02/24/2012 08:41 AM, Stefan Hajnoczi wrote:
> >
> > I dont think that it is cpu intense. All user pages are zeroed anyway, but at allocation time it shouldnt be a big difference in terms of cpu power.
>
> It's easy to find a scenario where eagerly zeroing pages is wasteful.
> Imagine a process that uses all of physical memory. Once it
> terminates the system is going to run processes that only use a small
> set of pages. It's pointless zeroing all those pages if we're not
> going to use them anymore.
In the long term, we will use them, except if the guest is completely idle.
The scenario in which zeroing is expensive is when the page is refilled
through DMA. In that case the zeroing was wasted. This is a pretty
common scenario in pagecache intensive workloads.
--
error compiling committee.c: too many arguments to function
next prev parent reply other threads:[~2012-02-28 13:17 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-23 15:40 [Qemu-devel] linux guests and ksm performance Peter Lieven
2012-02-23 16:42 ` Stefan Hajnoczi
2012-02-23 18:39 ` Javier Guerra Giraldez
2012-02-23 19:08 ` peter.lieven@gmail.com
2012-02-24 6:41 ` Stefan Hajnoczi
2012-02-24 6:53 ` Stefan Hajnoczi
2012-02-24 7:23 ` Stefan Hajnoczi
2012-02-24 7:43 ` Peter Lieven
2012-02-28 11:45 ` Peter Lieven
[not found] ` <4F4CBE7C.8040304@dlh.net>
[not found] ` <CAJSP0QWj0fJT-P-yHKicz4mGyhW4RnWXgimNad07JYXew5qmZw@mail.gmail.com>
2012-02-28 12:16 ` Peter Lieven
2012-02-28 13:16 ` Avi Kivity [this message]
2012-02-28 13:20 ` Peter Lieven
2012-02-28 13:56 ` Avi Kivity
2012-02-24 7:04 ` Gleb Natapov
2012-02-28 13:14 ` Avi Kivity
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