From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37501) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aK1S3-0006Uk-TP for qemu-devel@nongnu.org; Fri, 15 Jan 2016 05:17:52 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aK1S0-0002EG-M6 for qemu-devel@nongnu.org; Fri, 15 Jan 2016 05:17:51 -0500 Received: from szxga03-in.huawei.com ([119.145.14.66]:55472) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aK1Rz-0002D5-Sd for qemu-devel@nongnu.org; Fri, 15 Jan 2016 05:17:48 -0500 References: <1452851297-11198-1-git-send-email-liang.z.li@intel.com> From: Hailiang Zhang Message-ID: <5698C735.3020409@huawei.com> Date: Fri, 15 Jan 2016 18:17:25 +0800 MIME-Version: 1.0 In-Reply-To: <1452851297-11198-1-git-send-email-liang.z.li@intel.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] migration: not send zero page header in ram bulk stage List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Liang Li , qemu-devel@nongnu.org Cc: amit.shah@redhat.com, pbonzini@redhat.com, peter.huangpeng@huawei.com, dgilbert@redhat.com, quintela@redhat.com On 2016/1/15 17:48, Liang Li wrote: > Now that VM's RAM pages are initialized to zero, (VM's RAM is allcated > with the mmap() and MAP_ANONYMOUS option, or mmap() without MAP_SHARED > if hugetlbfs is used.) so there is no need to send the zero page header > to destination. > It seems that this patch is incorrect, if the no-zero pages are zeroed again during !ram_bulk_stage, we didn't send the new zeroed page, there will be an error. > For guest just uses a small portions of RAM, this change can avoid > allocating all the guest's RAM pages in the destination node after > live migration. Another benefit is destination QEMU can save lots of > CPU cycles for zero page checking. > > Signed-off-by: Liang Li > --- > migration/ram.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/migration/ram.c b/migration/ram.c > index 4e606ab..c4821d1 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -705,10 +705,12 @@ static int save_zero_page(QEMUFile *f, RAMBlock *block, ram_addr_t offset, > > if (is_zero_range(p, TARGET_PAGE_SIZE)) { > acct_info.dup_pages++; > - *bytes_transferred += save_page_header(f, block, > - offset | RAM_SAVE_FLAG_COMPRESS); > - qemu_put_byte(f, 0); > - *bytes_transferred += 1; > + if (!ram_bulk_stage) { > + *bytes_transferred += save_page_header(f, block, offset | > + RAM_SAVE_FLAG_COMPRESS); > + qemu_put_byte(f, 0); > + *bytes_transferred += 1; > + } > pages = 1; > } > >