From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=38158 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PaZwA-00029D-RA for qemu-devel@nongnu.org; Wed, 05 Jan 2011 15:26:28 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PaZw9-0005Gt-Og for qemu-devel@nongnu.org; Wed, 05 Jan 2011 15:26:26 -0500 Received: from e4.ny.us.ibm.com ([32.97.182.144]:47598) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PaZw9-0005G7-MG for qemu-devel@nongnu.org; Wed, 05 Jan 2011 15:26:25 -0500 Received: from d01dlp02.pok.ibm.com (d01dlp02.pok.ibm.com [9.56.224.85]) by e4.ny.us.ibm.com (8.14.4/8.13.1) with ESMTP id p05K8co1012699 for ; Wed, 5 Jan 2011 15:08:39 -0500 Received: from d01relay04.pok.ibm.com (d01relay04.pok.ibm.com [9.56.227.236]) by d01dlp02.pok.ibm.com (Postfix) with ESMTP id 59B7E4DE8040 for ; Wed, 5 Jan 2011 15:23:32 -0500 (EST) Received: from d03av05.boulder.ibm.com (d03av05.boulder.ibm.com [9.17.195.85]) by d01relay04.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p05KQL1d195282 for ; Wed, 5 Jan 2011 15:26:21 -0500 Received: from d03av05.boulder.ibm.com (loopback [127.0.0.1]) by d03av05.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p05KQKIn000478 for ; Wed, 5 Jan 2011 13:26:20 -0700 Message-ID: <4D24D3EB.1080702@linux.vnet.ibm.com> Date: Wed, 05 Jan 2011 14:26:19 -0600 From: Michael Roth MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH] add MADV_DONTFORK to guest physical memory References: <20100915170824.GL5981@random.random> <20110105151012.GC15823@random.random> <4D24B22C.4010302@linux.vnet.ibm.com> <20110105195430.GF15823@random.random> In-Reply-To: <20110105195430.GF15823@random.random> 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: Andrea Arcangeli Cc: Blue Swirl , =?ISO-8859-1?Q?Andreas_F=E4rber?= , Anthony Liguori , Alexander Graf , "qemu-devel@nongnu.org Developers" On 01/05/2011 01:54 PM, Andrea Arcangeli wrote: > Hello everyone, > > On Wed, Jan 05, 2011 at 08:44:38PM +0100, Alexander Graf wrote: >> >> On 05.01.2011, at 19:02, Michael Roth wrote: >> >>> On 01/05/2011 09:10 AM, Andrea Arcangeli wrote: >>>> The bug is still there so I rediffed the old patch against current >>>> code. >>>> >>>> On a related topic: could somebody give me advice on how to implement >>>> a command line (command line seems enough, the other option would be >>>> monitor command) to make the MADV_MERGEABLE conditional? I got KSM on >>>> THP working fine but KSM may decrease performance by increasing the >>>> number of copy on write and by splitting hugepages, so we'd like to be >>>> able to turn off KSM on a per-VM basis (not on the whole host, which >>>> of course we already can by setting /sys/kernel/mm/ksm/run to 0) so >>>> that high perf VMs will keep running at maximum speed with KSM off but >>>> others may still benefit from KSM. For that I need to make the below >>>> MADV_MERGEABLE madvise conditional to something and the code itself >>>> will be trivial, we've just to converge on a command line option >>>> (hopefully quickly ;). >>> >>> There was a -mem_prealloc option added a while back to set MAP_POPULATE on memory mapped in via the -mem-path option. So an analogous -mem_nomerge option or something along that line seems reasonable for conditionally unsetting QEMU_MADV_MERGEABLE. >>> >>> And for consistency you should probably make both your proposed changes for -mem-path'd memory as well. >> >> Why not clean up all that mess and introduce a new -mem option that would just take all of the several options as parameters? >> >> -mem size=512,populate=on,ksm=off >> >> and default -m to something reasonable with the new syntax. > > I'm neutral... so feel free to decide what I should implement ;). Have to agree the consolidated approach definitely seems nicer. > > One comment on combining -m ksm=off (or -mem_nomerge) with > -mem-path. It seems unnecessary because ksm can't be turned on on > VM_HUGETLB vmas (MADV_MERGEABLE will return -EINVAL) and mem-path only > makes sense if used in combination with hugetlbfs (which sets > VM_HUGETLB of course). > Yah you're right, but I've seen several discussions about using mempath for tmpfs/ram-backed files for things like numa/zram/etc so tend to think of it as something potentially more than just a hook for hugetlbfs, which is becoming less and less useful. But the MADV_DONTFORK stuff should still be immediately applicable.