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Re: [Qemu-devel] [PATCHv3 7/9] migration: do not sent zero pages in bulk
From: |
Peter Lieven |
Subject: |
Re: [Qemu-devel] [PATCHv3 7/9] migration: do not sent zero pages in bulk stage |
Date: |
Thu, 21 Mar 2013 20:44:02 +0100 |
Am 21.03.2013 um 20:26 schrieb Eric Blake <address@hidden>:
> 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)'.
If its inside then bytes_sent will be -1 at the end if we skip a page. This
would lead
to the raw page being sent. This way it is 0 what I think is correct.
>
> Do we want to add a new migration statistic counter of how many zero
> pages we omitted sending during the bulk stage?
You mean sth like skipped zero pages?
I was also thinking of renaming dup_pages into zero_pages in the statistics,
but this could break someone relying on it so I left it as is.
Peter
>
> --
> Eric Blake eblake redhat com +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
- [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
- [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
- [Qemu-devel] [PATCHv3 3/9] buffer_is_zero: use vector optimizations if possible, Peter Lieven, 2013/03/21