From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id 59C966B0069 for ; Wed, 2 Nov 2011 11:45:08 -0400 (EDT) Message-ID: <4EB16572.70209@redhat.com> Date: Wed, 02 Nov 2011 17:44:50 +0200 From: Avi Kivity MIME-Version: 1.0 Subject: Re: [GIT PULL] mm: frontswap (for 3.2 window) References: <75efb251-7a5e-4aca-91e2-f85627090363@default> <20111027215243.GA31644@infradead.org> <1319785956.3235.7.camel@lappy> <552d2067-474d-4aef-a9a4-89e5fd8ef84f@default> <20111031181651.GF3466@redhat.com> <1320142590.7701.64.camel@dabdike> In-Reply-To: <1320142590.7701.64.camel@dabdike> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: James Bottomley Cc: Andrea Arcangeli , Dan Magenheimer , Pekka Enberg , Cyclonus J , Sasha Levin , Christoph Hellwig , David Rientjes , Linus Torvalds , linux-mm@kvack.org, LKML , Andrew Morton , Konrad Wilk , Jeremy Fitzhardinge , Seth Jennings , ngupta@vflare.org, Chris Mason , JBeulich@novell.com, Dave Hansen , Jonathan Corbet On 11/01/2011 12:16 PM, James Bottomley wrote: > Actually, I think there's an unexpressed fifth requirement: > > 5. The optimised use case should be for non-paging situations. > > The problem here is that almost every data centre person tries very hard > to make sure their systems never tip into the swap zone. A lot of > hosting datacentres use tons of cgroup controllers for this and > deliberately never configure swap which makes transcendent memory > useless to them under the current API. I'm not sure this is fixable, > but it's the reason why a large swathe of users would never be > interested in the patches, because they by design never operate in the > region transcended memory is currently looking to address. > > This isn't an inherent design flaw, but it does ask the question "is > your design scope too narrow?" If you look at cleancache, then it addresses this concern - it extends pagecache through host memory. When dropping a page from the tail of the LRU it first goes into tmem, and when reading in a page from disk you first try to read it from tmem. However in many workloads, cleancache is actually detrimental. If you have a lot of cache misses, then every one of them causes a pointless vmexit; considering that servers today can chew hundreds of megabytes per second, this adds up. On the other side, if you have a use-once workload, then every page that falls of the tail of the LRU causes a vmexit and a pointless page copy. -- error compiling committee.c: too many arguments to function -- 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