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Re: [Qemu-devel] RFC migration of zero pages
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] RFC migration of zero pages |
Date: |
Fri, 01 Feb 2013 18:03:43 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 |
Il 31/01/2013 09:33, Orit Wasserman ha scritto:
>> > If my above assumption that the guest reads unmapped memory as zeroes is
>> > right, this mapping
>> > is not necessary in the case of a zero dup page.
>> >
>> > We just have to make sure that we are still in the very first round when
>> > deciding not to sent
>> > a zero page, because otherwise it could be a page that has become zero
>> > during migration and
>> > this of course has to be transferred.
> OK, so if we won't send the pages than it won't be allocate in the dst and it
> can improve both
> memory usage and reduce cpu consumption on it.
> That can be good for over commit scenario.
We don't allocate zero pages in the destination:
#ifndef _WIN32
if (ch == 0 &&
(!kvm_enabled() || kvm_has_sync_mmu()) &&
getpagesize() <= TARGET_PAGE_SIZE) {
qemu_madvise(host, TARGET_PAGE_SIZE, QEMU_MADV_DONTNEED);
}
#endif
Paolo