From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 8 Mar 2007 13:19:30 +0100 From: Nick Piggin Subject: Re: [RFC][PATCH] mm: fix page_mkclean() vs non-linear vmas Message-ID: <20070308121930.GB22781@wotan.suse.de> References: <1173273562.6374.175.camel@twins> <20070307133649.GF18704@wotan.suse.de> <1173275532.6374.183.camel@twins> <1173278067.6374.188.camel@twins> <20070307150102.GH18704@wotan.suse.de> <1173286682.6374.191.camel@twins> <1173353824.9438.15.camel@twins> <1173355903.9438.18.camel@twins> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1173355903.9438.18.camel@twins> Sender: owner-linux-mm@kvack.org Return-Path: To: Peter Zijlstra Cc: Miklos Szeredi , akpm@linux-foundation.org, mingo@elte.hu, linux-mm@kvack.org, linux-kernel@vger.kernel.org, benh@kernel.crashing.org, jdike@addtoit.com, hugh@veritas.com, torvalds@linux-foundation.org List-ID: On Thu, Mar 08, 2007 at 01:11:43PM +0100, Peter Zijlstra wrote: > On Thu, 2007-03-08 at 12:48 +0100, Miklos Szeredi wrote: > > > However this still leaves the non-linear reclaim (Nick pointed it out as > > > a potential DoS and other people have corroborated this). I have no idea > > > on that to do about that. > > > > OK, but that is a completely different problem, not affecting > > page_mkclean() or msync(). > > > > And it doesn't sound too hard to solve: when current algorithm doesn't > > seem to be making progress, then it will have to be done the hard way, > > searching for for all nonlinear ptes of a page to unmap. > > Ah, you see, but that is when you've already lost. > > The DoS is about the computational complexity of the reclaim, not if it > will ever come out of it with free pages. If we really want to, we could limit it to mlock for !root. This is a reasonable way to solve the problem, and UML could fall back on vma emulated version if they didn't want to use mlock memory... Or we could limit the size/number of nonlinear vmas that could be created. But just quietly, I think there are probably a lot of other ways to perform a local DoS anyway ;) -- 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