From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [PATCH] Update Unevictable LRU and Mlocked Pages documentation From: Lee Schermerhorn In-Reply-To: <4891C8BC.1020509@linux-foundation.org> References: <1217452439.7676.26.camel@lts-notebook> <4891C8BC.1020509@linux-foundation.org> Content-Type: text/plain Date: Thu, 31 Jul 2008 10:43:49 -0400 Message-Id: <1217515429.6507.7.camel@lts-notebook> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Christoph Lameter Cc: Andrew Morton , linux-mm , KOSAKI Motohiro , Kamezawa Hiroyuki , Rik van Riel , Nick Piggin List-ID: On Thu, 2008-07-31 at 09:14 -0500, Christoph Lameter wrote: > > +Why maintain unevictable pages on an additional LRU list? Primarily because > > +we want to be able to migrate unevictable pages between nodes--for memory > > +deframentation, workload management and memory hotplug. The linux kernel can > > +only migrate pages that it can successfully isolate from the lru lists. > > +Therefore, we want to keep the unevictable pages on an lru-like list, where > > +they can be found by isolate_lru_page(). > > The primary motivation for me was to get rid of the useless scanning > of pages under memory pressure which led to live lock scenarios. > mlocked pages are migratable now so the changes do not really change > anything there. The unevictable lists are also necessary to spill > pages back to the regular LRUs when unevictable pages become evictable > again. Hi, Christoph: Yes, mlocked pages are migratable now [before the unevictable lru/mlocked pages patches], but that's because they reside on the LRU lists. If we just moved them off to a list that isn't known to isolate_lru_page(), it wouldn't find them and they wouldn't be migrated. So, I want to keep them on an LRU-like list so that they remain migratable. I was just explaining that rationale in the doc. Thanks for reviewing, 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