From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Hansen Subject: Re: [RFC/T/D][PATCH 2/2] Linux/Guest cooperative unmapped page cache control Date: Mon, 14 Jun 2010 08:33:16 -0700 Message-ID: <1276529596.6437.7216.camel@nimitz> References: <20100608155140.3749.74418.sendpatchset@L34Z31A.ibm.com> <20100608155153.3749.31669.sendpatchset@L34Z31A.ibm.com> <4C10B3AF.7020908@redhat.com> <20100610142512.GB5191@balbir.in.ibm.com> <1276214852.6437.1427.camel@nimitz> <20100611045600.GE5191@balbir.in.ibm.com> <4C15E3C8.20407@redhat.com> <20100614084810.GT5191@balbir.in.ibm.com> <4C16233C.1040108@redhat.com> <20100614125010.GU5191@balbir.in.ibm.com> <4C162846.7030303@redhat.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: balbir@linux.vnet.ibm.com, kvm , linux-mm@kvack.org, linux-kernel@vger.kernel.org To: Avi Kivity Return-path: In-Reply-To: <4C162846.7030303@redhat.com> Sender: owner-linux-mm@kvack.org List-Id: kvm.vger.kernel.org On Mon, 2010-06-14 at 16:01 +0300, Avi Kivity wrote: > If we drop unmapped pagecache pages, we need to be sure they can be > backed by the host, and that depends on the amount of sharing. You also have to set up the host up properly, and continue to maintain it in a way that finds and eliminates duplicates. I saw some benchmarks where KSM was doing great, finding lots of duplicate pages. Then, the host filled up, and guests started reclaiming. As memory pressure got worse, so did KSM's ability to find duplicates. At the same time, I see what you're trying to do with this. It really can be an alternative to ballooning if we do it right, since ballooning would probably evict similar pages. Although it would only work in idle guests, what about a knob that the host can turn to just get the guest to start running reclaim? -- Dave -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org