From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 30 Jan 2006 13:59:40 -0800 (PST) From: Christoph Lameter Subject: Re: [PATCH] Zone reclaim: Allow modification of zone reclaim behavior In-Reply-To: <20060130134554.500b73a3.akpm@osdl.org> Message-ID: References: <20060130134554.500b73a3.akpm@osdl.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: linux-mm@kvack.org List-ID: On Mon, 30 Jan 2006, Andrew Morton wrote: > The proliferating /proc configurability is a worry. It'll confuse people > and people just won't know that it's there and it's yet another question > which maintenance people need to ask end-users during problem resolution. > > Is there not some means by which we can simply get these things right? I wish I knew some other way to do this. We will have to do significant changes to the VM to even have the data available to make the proper decisions in these settings. See my zone based counter patches from before Christmas. These allow to get rid of the reclaim_interval but are so extensive you would not want them for 2.6.16. More brainwork is needed after the counters are in to figure out way to make the other knobs unnecessary. > Why wouldn't we want to perform writeback or swapout during zone reclaim? Because that will reduce performance. If writeback is performed during reclaim then a process cannot dirty all of available memory. It will be throttled after using up all of a nodes memory. This is a significant regression from current performance. If you do swapout then the process is restricted to a node and will start swapping if more memory starts being used than a node has avalable. This is going to drastically reduce performance. zone_reclaim in its default configuration is simply throwing out pages that have no references left. These are pagecache pages that may be left from a copy operation or from an application that has terminated. > Why wouldn't we want to reclaim slab during zone reclaim? Because its too expensive to do and because slab reclaim is not able to cleanly reclaim per zone right now. It does a global shrink operation on nodes that may still have lots of memory available. We can skip some of these for 2.6.16 if you do not want the knobs. The default behavior without the knobs should be fine for most cases. -- 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