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Re: [Qemu-devel] RFC migration of zero pages
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From: |
Paolo Bonzini |
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Subject: |
Re: [Qemu-devel] RFC migration of zero pages |
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Date: |
Fri, 01 Feb 2013 17:58:28 +0100 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 |
Il 31/01/2013 10:48, Gleb Natapov ha scritto:
>> Also I notice that the bottle neck in migrating unmapped pages is the
>> detection of those pages
>> because we map the pages in order to check them, for a large guest this is
>> very expensive as mapping a page
>> results in a page fault in the host.
>> So what will be very helpful is actually locating those pages without
>> mapping them
>> which looks very complicated.
>>
> What is wrong with mincore()?
As Avi said, it returns false if the memory is in swap.
Note that while we do take a page fault, the recent kernel patch to
introduce a huge zero page might have reduced the cost in terms of both
clear_page and cache misses.
Paolo