From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sat, 17 Jun 2000 00:05:27 -0300 Subject: Re: kswapd eating too much CPU on ac16/ac18 Message-ID: <20000617000527.A5485@cesarb.personal> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: ; from riel@conectiva.com.br on Fri, Jun 16, 2000 at 12:08:06PM -0300 From: Cesar Eduardo Barros Sender: owner-linux-mm@kvack.org Return-Path: To: Rik van Riel Cc: Mike Galbraith , Alan Cox , Cesar Eduardo Barros , linux-kernel , linux-mm@kvack.org List-ID: On Fri, Jun 16, 2000 at 12:08:06PM -0300, Rik van Riel wrote: > On Fri, 16 Jun 2000, Mike Galbraith wrote: > > On Wed, 14 Jun 2000, Alan Cox wrote: > > > > > Im interested to know if ac9/ac10 is the slow->fast change point > > > > ac5 is definately the breaking point. ac5 doesn't survive make > > -j30.. starts swinging it's VM machette at everything in sight. > > Reversing the VM changes to ac4 restores throughput to test1 > > levels (11 minute build vs 21-26 minutes for everything > > forward). > > > > Exact tested reversals below. FWIW, page aging doesn't seem to > > be the problem. I disabled that in ac17 and saw zero > > difference. (What may or not be a hint is that the /* Let > > shrink_mmap handle this swapout. */ bit in vmscan.c does make a > > consistent difference. Reverting that bit alone takes a minimum > > of 4 minutes off build time) > > Interesting. Not delaying the swapout IO completely broke > performance under the tests I did here... > > Delayed swapout vs. non-delayed swapouts was the difference > between 300 swapouts/s vs. 700 swapouts/s (under a load > with 400 swapins/s). I can understand it... When you wake up kswapd you need more memory, and if you don't free it you will be called again. And again. And again. (leaf is a slow box; both top and vmstat eat 20% CPU each with 1 second updates all the time). So it does waste more time. Worst case (dpkg --install) in ac4 gets kswapd at about 5%. Which considering that top or vmstat use 20% is low enough. Also it gets more throughput because it has no need to waste time thinking. With ac4 I get the HDD light full on during the worse moments; with ac16/18 it just sits there in kswapd and the light blinks at about 1Hz. > OTOH, I can imagine it being better if you have a very small > LRU cache, something like less than 1/2 MB. You can imagine it being better in some random rare condition I don't care about. People have been noticing speed problems related to kswapd. This is not microkernel research. -- Cesar Eduardo Barros cesarb@nitnet.com.br cesarb@dcc.ufrj.br -- 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.eu.org/Linux-MM/