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From: Juan Quintela <quintela@redhat.com>
In-Reply-To: <20170327092350.GH11497@pxdev.xzpeter.org> (Peter Xu's message of
	"Mon, 27 Mar 2017 17:23:50 +0800")
References: <20170323204544.12015-1-quintela@redhat.com>
	<20170323204544.12015-12-quintela@redhat.com>
	<20170327092350.GH11497@pxdev.xzpeter.org>
Reply-To: quintela@redhat.com
Date: Tue, 28 Mar 2017 20:43:37 +0200
Message-ID: <8737dxqm1y.fsf@secure.mitica>
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Subject: Re: [Qemu-devel] [PATCH 11/51] ram: Move dup_pages into RAMState
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To: Peter Xu <peterx@redhat.com>
Cc: qemu-devel@nongnu.org, dgilbert@redhat.com

Peter Xu <peterx@redhat.com> wrote:
> On Thu, Mar 23, 2017 at 09:45:04PM +0100, Juan Quintela wrote:
>> Once there rename it to its actual meaning, zero_pages.
>> 
>> Signed-off-by: Juan Quintela <quintela@redhat.com>
>> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>
> Reviewed-by: Peter Xu <peterx@redhat.com>
>
> Will post a question below though (not directly related to this patch
> but context-wide)...
>>  {
>>      int pages = -1;
>>  
>>      if (is_zero_range(p, TARGET_PAGE_SIZE)) {
>> -        acct_info.dup_pages++;
>> +        rs->zero_pages++;
>>          *bytes_transferred += save_page_header(f, block,
>>                                                 offset | RAM_SAVE_FLAG_COMPRESS);
>>          qemu_put_byte(f, 0);
>> @@ -822,11 +826,11 @@ static int ram_save_page(RAMState *rs, MigrationState *ms, QEMUFile *f,
>>              if (bytes_xmit > 0) {
>>                  acct_info.norm_pages++;
>>              } else if (bytes_xmit == 0) {
>> -                acct_info.dup_pages++;
>> +                rs->zero_pages++;
>
> This code path looks suspicous... since iiuc currently it should only
> be triggered by RDMA case, and I believe here qemu_rdma_save_page()
> should have met something wrong (so that it didn't return with
> RAM_SAVE_CONTROL_DELAYED). Then is it correct we do increase zero page
> counting unconditionally here? (hmm, the default bytes_xmit is zero as
> well...)

My head hurts at this point.
ok.  bytse_xmit can only be zero if we called qemu_rdma_save_page() with
size=0 or there has been an RDMA error.  We ver call the function with
size = 0.  And if there is one error, we are in very bady shape already.

> Another thing is that I see when RDMA is enabled we are updating
> accounting info with acct_update_position(), while we updated it here
> as well. Is this an issue of duplicated accounting?

I think stats and rdma are not right.  I have to check more that.

Thanks, Juan.