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Date: Mon, 04 Nov 2013 10:29:25 +0100
From: Peter Lieven <pl@kamp.de>
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Subject: Re: [Qemu-devel] [RESEND][PATCH] migration: drop MADVISE_DONT_NEED
 for incoming zero pages
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To: quintela@redhat.com
Cc: pbonzini@redhat.com, haoyu.zhang@huawei.com, qemu-devel@nongnu.org, afaerber@suse.de, xiaoguangrong@linux.vnet.ibm.com

On 24.10.2013 12:07, Juan Quintela wrote:
> Peter Lieven <pl@kamp.de> wrote:
>> The madvise for zeroed out pages was introduced when every transferred
>> zero page was memset to zero and thus allocated. Since commit
>> 211ea740 we check for zeroness of a target page before we memset
>> it to zero. Additionally we memmap target memory so it is essentially
>> zero initialized (except for e.g. option roms and bios which are loaded
>> into target memory although they shouldn't).
>>
>> It was reported recently that this madvise causes a performance degradation
>> in some situations. As the madvise should only be called rarely and if it's called
>> it is likely on a busy page (it was non-zero and changed to zero during migration)
>> drop it completely.
> Reviewed-by: Juan Quintela <quintela@redhat.com>
>
> I take it.  I am on KVM Forum/LinuxCon this week.  Will send when back
> at home.
Ping

Peter