From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from aa.eps.jhu.edu (aa.eps.jhu.edu [128.220.24.92]) by jhmail.hcf.jhu.edu (PMDF V5.2-31 #37929) with ESMTP id <01JJAUVWS8AWFANY9M@jhmail.hcf.jhu.edu> for linux-mm@kvack.org; Thu, 9 Dec 1999 14:39:00 EDT Date: Thu, 09 Dec 1999 14:37:39 -0500 (EST) From: afei@jhu.edu Subject: Re: Motivation for page replace alg.? In-reply-to: <199912091021.FAA21828@bowery.psl.cs.columbia.edu> Message-id: MIME-version: 1.0 Content-type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Chris Vaill Cc: linux-mm@kvack.org List-ID: Chris, we have done some analysis on this problem. Please check out the online document about linux memory management at: http://aa.eps.jhu.edu/~feiliu/Linux sorry about the readability, it is converted from word. I will work on the layout later, but the content is there. Fei On Thu, 9 Dec 1999, Chris Vaill wrote: > I'm a kernel newbie, and I apologize if my question is answered by > easily accessible docs, but I couldn't find any such answers in my > search. > > I've been looking into the swap out routines, and in particular their > behavior when faced with several competing processes aggressively > allocating and using memory (more memory, collectively, than is > physically available). I've found that this results in repeated > drastic swings in rss for each process over time. > > As far as I can tell, this results from the way swap_cnt is separated > from rss. A victim process is chosen because it has the highest > swap_cnt, but as its rss falls, the swap_cnt stays high, so the same > victim process is chosen over and over again until no more pages can > be swapped from that process, and swap_cnt is zeroed. From my (very > naive) perspective, it seems that always choosing the same victim > process for swapping would not result in a good approximation of LRU. > > My questions are, is my read of the code correct here, and is this the > intended behavior of the page replacement algorithm? If so, what is > the motivation? Is this based on some existing mm research, or > informal observation and testing, or something else entirely? > > I've heard it mentioned that the swap routines were not meant to deal > with trashing procs, which is basically what I am testing here. > Obviously the swap routines work pretty well for normal, well-behaved > procs; I'm just trying to get a little insight into the design process > here. > > Thanks for any info or pointers anyone can provide. > > -Chris > > P.S. I did my testing on 2.2.13, but it is my understanding that the > algorithm is the same in the 2.3 kernels. Smack me if this is not the > case. > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://humbolt.geo.uu.nl/Linux-MM/ > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://humbolt.geo.uu.nl/Linux-MM/