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Re: [Qemu-devel] linux guests and ksm performance
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] linux guests and ksm performance |
Date: |
Fri, 24 Feb 2012 06:41:56 +0000 |
On Thu, Feb 23, 2012 at 7:08 PM, address@hidden <address@hidden> wrote:
>
>
>
>
> Stefan Hajnoczi <address@hidden> schrieb:
>
>>On Thu, Feb 23, 2012 at 3:40 PM, Peter Lieven <address@hidden> wrote:
>>> However, in a virtual machine I have not observed the above slow down
>>to
>>> that extend
>>> while the benefit of zero after free in a virtualisation environment
>>is
>>> obvious:
>>>
>>> 1) zero pages can easily be merged by ksm or other technique.
>>> 2) zero (dup) pages are a lot faster to transfer in case of
>>migration.
>>
>>The other approach is a memory page "discard" mechanism - which
>>obviously requires more code changes than zeroing freed pages.
>>
>>The advantage is that we don't take the brute-force and CPU intensive
>>approach of zeroing pages. It would be like a fine-grained ballooning
>>feature.
>>
>
> 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.
Stefan
- [Qemu-devel] linux guests and ksm performance, Peter Lieven, 2012/02/23
- Re: [Qemu-devel] linux guests and ksm performance, Stefan Hajnoczi, 2012/02/23
- Re: [Qemu-devel] linux guests and ksm performance, Javier Guerra Giraldez, 2012/02/23
- Re: [Qemu-devel] linux guests and ksm performance, address@hidden, 2012/02/23
- Re: [Qemu-devel] linux guests and ksm performance,
Stefan Hajnoczi <=
- Re: [Qemu-devel] linux guests and ksm performance, Stefan Hajnoczi, 2012/02/24
- Re: [Qemu-devel] linux guests and ksm performance, Stefan Hajnoczi, 2012/02/24
- Re: [Qemu-devel] linux guests and ksm performance, Peter Lieven, 2012/02/24
- Re: [Qemu-devel] linux guests and ksm performance, Peter Lieven, 2012/02/28
- Message not available
- Message not available
- Re: [Qemu-devel] linux guests and ksm performance, Peter Lieven, 2012/02/28
- Re: [Qemu-devel] linux guests and ksm performance, Avi Kivity, 2012/02/28
- Re: [Qemu-devel] linux guests and ksm performance, Peter Lieven, 2012/02/28
- Re: [Qemu-devel] linux guests and ksm performance, Avi Kivity, 2012/02/28
Re: [Qemu-devel] linux guests and ksm performance, Gleb Natapov, 2012/02/24
Re: [Qemu-devel] linux guests and ksm performance, Avi Kivity, 2012/02/28