From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=41200 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PNnwz-0007Fr-TS for qemu-devel@nongnu.org; Wed, 01 Dec 2010 09:46:31 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PNnwy-000865-Di for qemu-devel@nongnu.org; Wed, 01 Dec 2010 09:46:29 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48422) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PNnwx-00084h-Ut for qemu-devel@nongnu.org; Wed, 01 Dec 2010 09:46:28 -0500 Message-ID: <4CF65FBB.3020406@redhat.com> Date: Wed, 01 Dec 2010 16:46:19 +0200 From: Avi Kivity MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: [PATCH 10/10] Maintaing number of dirty pages References: <411b3f89b6b79b429686bd1b1fa188ba55b6c6f7.1290552026.git.quintela@redhat.com> <4CF45DE0.8020701@codemonkey.ws> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Juan Quintela Cc: qemu-devel@nongnu.org On 11/30/2010 04:46 PM, Juan Quintela wrote: > Anthony Liguori wrote: > > On 11/23/2010 05:03 PM, Juan Quintela wrote: > >> From: Juan Quintela > >> > >> Calculate the number of dirty pages takes a lot on hosts with lots > >> of memory. Just maintain how many pages are dirty. Only sync bitmaps > >> if number is small enough. > >> > > > > There needs to be numbers that justify this as part of the commit message. > > They are on patch 0/6. > > Additionally, with 64GB of RAM, this bitmap is HUGE, having to walk over > it in each ram_save_live() call is too onerous. It's not so huge. It's scaled down by a factor of 8 * 4096 = 32K. So it's a 2MB bitmap. If kept as a bitmap and accessed in longs, it can be read in less than a millisecond. An optimization can be to look at the previous ram_save_live (which had to walk the bitmap). If old_nr_dirty > 4*target_nr_dirty, assume we need one more pass and don't scan the bitmap. Another optimization is to stop the count when we reach the target; instead of ram_save_remaining() have a ram_save_may_stop() which counts the number of dirty bits until it reaches target_nr_dirty or exhausts the bitmap. -- error compiling committee.c: too many arguments to function