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Re: [Qemu-devel] [PATCHv3 7/9] migration: do not sent zero pages in bulk
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCHv3 7/9] migration: do not sent zero pages in bulk stage |
Date: |
Thu, 21 Mar 2013 13:26:35 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4 |
On 03/21/2013 09:57 AM, Peter Lieven wrote:
> during bulk stage of ram migration if a page is a
> zero page do not send it at all.
> the memory at the destination reads as zero anyway.
>
> even if there is an madvise with QEMU_MADV_DONTNEED
> at the target upon receipt of a zero page I have observed
> that the target starts swapping if the memory is overcommitted.
> it seems that the pages are dropped asynchronously.
>
> Signed-off-by: Peter Lieven <address@hidden>
> ---
> arch_init.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
> if (is_zero_page(p)) {
> acct_info.dup_pages++;
> - bytes_sent = save_block_hdr(f, block, offset, cont,
> - RAM_SAVE_FLAG_COMPRESS);
> - qemu_put_byte(f, *p);
> - bytes_sent += 1;
> + if (!ram_bulk_stage) {
> + bytes_sent = save_block_hdr(f, block, offset, cont,
> + RAM_SAVE_FLAG_COMPRESS);
> + qemu_put_byte(f, 0);
> + }
> + bytes_sent++;
Logic is STILL wrong. I pointed out in v2 that bytes_sent should not be
incremented if you are not sending the page, so it needs to be inside
the 'if (!ram_bulk_stage)'.
Do we want to add a new migration statistic counter of how many zero
pages we omitted sending during the bulk stage?
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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- [Qemu-devel] [PATCHv3 0/9] buffer_is_zero / migration optimizations, Peter Lieven, 2013/03/21
- [Qemu-devel] [PATCHv3 1/9] move vector definitions to qemu-common.h, Peter Lieven, 2013/03/21
- [Qemu-devel] [PATCHv3 4/9] bitops: use vector algorithm to optimize find_next_bit(), Peter Lieven, 2013/03/21
- [Qemu-devel] [PATCHv3 8/9] migration: do not search dirty pages in bulk stage, Peter Lieven, 2013/03/21
- [Qemu-devel] [PATCHv3 7/9] migration: do not sent zero pages in bulk stage, Peter Lieven, 2013/03/21
- Re: [Qemu-devel] [PATCHv3 7/9] migration: do not sent zero pages in bulk stage,
Eric Blake <=
- [Qemu-devel] [PATCHv3 2/9] cutils: add a function to find non-zero content in a buffer, Peter Lieven, 2013/03/21
- [Qemu-devel] [PATCHv3 9/9] migration: use XBZRLE only after bulk stage, Peter Lieven, 2013/03/21
- [Qemu-devel] [PATCHv3 5/9] migration: search for zero instead of dup pages, Peter Lieven, 2013/03/21
- [Qemu-devel] [PATCHv3 6/9] migration: add an indicator for bulk state of ram migration, Peter Lieven, 2013/03/21