From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sun, 22 Sep 2002 01:49:46 +0100 (BST) From: Hugh Dickins Subject: Re: overcommit stuff In-Reply-To: <3D8D066F.1B45E3EA@digeo.com> Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: Alan Cox , "linux-mm@kvack.org" List-ID: On Sat, 21 Sep 2002, Andrew Morton wrote: > Hugh Dickins wrote: > > On Sat, 21 Sep 2002, Andrew Morton wrote: > > > > > > running 10,000 tiobench threads I'm showing 23 gigs of > > > `Commited_AS'. Is this right? Those pages are shared, > > > and if they're not PROT_WRITEable then there's no way in > > > which they can become unshared? Seems to be excessively > > > pessimistic? > > > Committed_AS certainly errs on the pessimistic side, that's > > what it's about. How much swap do you have i.e. is 23GB > > committed impossible, or just surprising to you? Does the > > number go back to what it started off from when you kill > > off the tests? How are "those pages" allocated e.g. what > > mmap args? > > I have 7G physical, 4G swap. When I wondered if impossible, of course I was overlooking that you wouldn't be running with strict commit limitation, so "impossible" is quite difficult to reach. > "those pages" were just used by some scruffy perl script > running `./tiotest &' ten thousand times. I assume it's > shared executable text. When I run tiotest here, /proc//maps shows a little over 2MB of rwxp or rw-p areas, all to be counted in Committed_AS. So 23GB for 10,000 of them sounds reasonable. You think you have less PROT_WRITE or less MAP_PRIVATE than I'm seeing? > It seems very unlikely (impossible?) that those pages will > ever become unshared. I expect it's very unlikely (short of application bugs) that those pages would become unshared; but they have been mapped in such a way that the process is entitled to unshare them, therefore they have been counted. A good example of why Linux does not impose strict commit accounting, and why you may choose not to use Alan's strict accounting policy. Hugh -- 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/