From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id 8225A6B003D for ; Mon, 23 Mar 2009 14:55:52 -0400 (EDT) Subject: Re: [PATCH 0/2] Make the Unevictable LRU available on NOMMU From: Lee Schermerhorn In-Reply-To: <20090321102044.GA3427@cmpxchg.org> References: <1237565305.27431.48.camel@lts-notebook> <20090312100049.43A3.A69D9226@jp.fujitsu.com> <20090313173343.10169.58053.stgit@warthog.procyon.org.uk> <28c262360903131727l4ef41db5xf917c7c5eb4825a8@mail.gmail.com> <12759.1237566272@redhat.com> <1237573815.27431.122.camel@lts-notebook> <20090321102044.GA3427@cmpxchg.org> Content-Type: text/plain Date: Mon, 23 Mar 2009 16:07:40 -0400 Message-Id: <1237838860.7334.59.camel@lts-notebook> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Johannes Weiner Cc: David Howells , Minchan Kim , Andrew Morton , kosaki.motohiro@jp.fujitsu.com, torvalds@linux-foundation.org, peterz@infradead.org, nrik.Berkhan@ge.com, uclinux-dev@uclinux.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, riel@surriel.com List-ID: On Sat, 2009-03-21 at 11:20 +0100, Johannes Weiner wrote: > On Fri, Mar 20, 2009 at 02:30:15PM -0400, Lee Schermerhorn wrote: > > On Fri, 2009-03-20 at 16:24 +0000, David Howells wrote: > > > Lee Schermerhorn wrote: > > > > > > > I just want to point out [again :)] that removing the ramfs pages from > > > > the lru will prevent them from being migrated > > > > > > This is less of an issue for NOMMU kernels, since you can't migrate pages that > > > are mapped. > > > > > > Agreed. So, you could eliminate them [ramfs pages] from the lru for > > just the nommu kernels, if you wanted to go that route. > > These pages don't come with much overhead anymore when they sit on the > unevictable list, right? So I don't see much point in special casing > them all over the place. I agree: not much overhead; no NEED to special case. I was only agreeing with David, that it would be OK to keep them off the LRU for NOMMU kernels. > > I have a patchset that decouples the unevictable lru feature from > mlock, enables the latter on nommu and then makes sure ramfs pages go > immediately to the unevictable list so they don't need the scanner to > move them. This is just wiring up of features we already have. Yeah. I didn't do it that way, because I didn't see any benefit in doing that for ram disk pages. If one doesn't run vmscan, having the pages on the normal lru doesn't hurt. If you do need to run vmscan, moving them to the unevictable list from there seems the least of your problems :). And, doing in the pagevec flush function adds overhead to the fault path. Granted, it's amortized over PAGEVEC_SIZE pages. Would probably we worth measuring the performance cost. And any code size increase--NOMMU kernel users might care about that. > > I will sent this mondayish, need to test it more especially on a NOMMU > setup. Saw them. Will take a look... Lee -- 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