From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: Subtle MM bug References: Reply-To: zlatko@iskon.hr From: Zlatko Calusic Date: 07 Jan 2001 23:33:08 +0100 In-Reply-To: Rik van Riel's message of "Sun, 7 Jan 2001 19:37:06 -0200 (BRDT)" Message-ID: <87u27b3sd7.fsf@atlas.iskon.hr> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org Return-Path: To: Rik van Riel Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: Rik van Riel writes: > On 7 Jan 2001, Zlatko Calusic wrote: > > > Things go berzerk if you have one big process whose working set > > is around your physical memory size. > > "go berzerk" in what way? Does the system cause lots of extra > swap IO and does it make the system thrash where 2.2 didn't > even touch the disk ? > Well, I think yes. I'll do some testing on the 2.2 before I can tell you for sure, but definitely the system is behaving badly where I think it should not. > > Final effect is that physical memory gets extremely flooded with > > the swap cache pages and at the same time the system absorbs > > ridiculous amount of the swap space. > > This is mostly because Linux 2.4 keeps dirty pages in the > swap cache. Under Linux 2.2 a page would be deleted from the > swap cache when a program writes to it, but in Linux 2.4 it > can stay in the swap cache. > OK, I can buy that. > Oh, and don't forget that pages in the swap cache can also > be resident in the process, so it's not like the swap cache > is "eating into" the process' RSS ;) > So far so good... A little bit weird but not alarming per se. > > For instance on my 192MB configuration, firing up the hogmem > > program which allocates let's say 170MB of memory and dirties it > > leads to 215MB of swap used. > > So that's 170MB of swap space for hogmem and 45MB for > the other things in the system (daemons, X, ...). > Yes, that's it. So it looks like all of my processes are on the swap. That can't be good. I mean, even Solaris (known to eat swap space like there's no tomorrow :)) would probably be more polite. > Sounds pretty ok, except maybe for the fact that now > Linux allocates (not uses!) a lot more swap space then > before and some people may need to add some swap space > to their system ... > Yes, I would say really a lot more. Big diffeence. Also, I don't see a diference between allocated and used swap space on the Linux. Could you elaborate on that? > > Now if 2.4 has worse _performance_ than 2.2 due to one > reason or another, that I'd like to hear about ;) > I'll get back to you later with more data. Time to boot 2.2. :) -- Zlatko -- 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/