From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 26 Oct 2007 18:11:19 +0100 Subject: Re: RFC/POC Make Page Tables Relocatable Message-ID: <20071026171119.GC19443@skynet.ie> References: <1193330774.4039.136.camel@localhost> <1193335725.24087.19.camel@localhost> <20071026161007.GA19443@skynet.ie> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: From: mel@skynet.ie (Mel Gorman) Sender: owner-linux-mm@kvack.org Return-Path: To: Ross Biro Cc: Dave Hansen , linux-mm@kvack.org, Mel Gorman List-ID: On (26/10/07 12:51), Ross Biro didst pronounce: > On 10/26/07, Mel Gorman wrote: > > I suspect this might be overkill from a memory fragmentation > > perspective. When grouping pages by mobility, page table pages are > > currently considered MIGRATE_UNMOVABLE. From what I have seen, they are > > I may be being dense, but the page migration code looks to me like it > just moves pages in a process from one node to another node with no > effort to touch the page tables. Exactly, if it was able to move arbitrary pagetable pages too, it would be useful. Page migrations traditional case is to move pages between nodes but memory hot-remove also uses it to move pages around a zone and there has been at least one other case which I'm coming to. > It would be easy to hook the code I > wrote into the page migration code, what I don't understand is when > the page tables should be migrated? >>From an external fragmentation point of view, they would be moved when a high-order allocation failued. Patches exist that do this sort of thing under the title "Memory Compaction" but they are not merged because they don't have a demonstratable use-case yet[1]. > Only when the whole process is > being migrated? When all the pages pointed to a page table are being > migrated? When any page pointed to by the page table is being > migrated? > If it was external fragmentation you were dealing with, a pagetable apge would be moved once it was found to be preventing a high-order (e.gh. hugepage) allocation from succeeding. [1] Intuitively, the use case would be that a hugepage allocation happened faster when moving pages around than reclaiming them. This situation does not happen often enough to justify the complexity of the code though. -- -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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