From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx147.postini.com [74.125.245.147]) by kanga.kvack.org (Postfix) with SMTP id 4126F6B004D for ; Fri, 20 Apr 2012 22:29:39 -0400 (EDT) Received: by dakh32 with SMTP id h32so14582458dak.9 for ; Fri, 20 Apr 2012 19:29:38 -0700 (PDT) Date: Sat, 21 Apr 2012 11:29:32 +0900 From: Takuya Yoshikawa Subject: Re: [PATCH] kvm: don't call mmu_shrinker w/o used_mmu_pages Message-Id: <20120421112932.3e4bd031d1defc8fe7915ade@gmail.com> In-Reply-To: References: <1334356721-9009-1-git-send-email-yinghan@google.com> <20120420151143.433c514e.akpm@linux-foundation.org> <4F91E8CC.5080409@redhat.com> <20120421105615.6b0b03640f7553060628d840@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mike Waychison Cc: Ying Han , Rik van Riel , Andrew Morton , Michal Hocko , Johannes Weiner , Mel Gorman , KAMEZAWA Hiroyuki , Hillf Danton , Hugh Dickins , Dan Magenheimer , linux-mm@kvack.org, kvm@vger.kernel.org, Avi Kivity , Marcelo Tosatti , Eric Northup On Fri, 20 Apr 2012 19:15:24 -0700 Mike Waychison wrote: > In our situation, we simple disable the shrinker altogether. My > understanding is that we EPT or NPT, the amount of memory used by > these tables is bounded by the size of guest physical memory, whereas > with software shadowed tables, it is bounded by the addresses spaces > in the guest. This bound makes it reasonable to not do any reclaim > and charge it as a "system overhead tax". IIRC, KVM's mmu_shrink is mainly for protecting the host from pathological guest without EPT or NPT. You can see Avi's summary: -- http://www.spinics.net/lists/kvm/msg65671.html === We should aim for the following: - normal operation causes very little shrinks (some are okay) - high pressure mostly due to kvm results in kvm being shrunk (this is a pathological case caused by a starting a guest with a huge amount of memory, and mapping it all to /dev/zero (or ksm), and getting the guest the create shadow mappings for all of it) - general high pressure is shared among other caches like dcache and icache The cost of reestablishing an mmu page can be as high as half a millisecond of cpu time, which is the reason I want to be conservative. === Thanks, Takuya -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org