From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 30 Jul 2007 06:35:28 +0200 From: Nick Piggin Subject: Re: [patch][rfc] remove ZERO_PAGE? Message-ID: <20070730043528.GC7222@wotan.suse.de> References: <20070727021943.GD13939@wotan.suse.de> <20070727055406.GA22581@wotan.suse.de> <20070730030806.GA17367@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org Return-Path: To: Linus Torvalds Cc: Andrew Morton , Hugh Dickins , Andrea Arcangeli , Linux Memory Management List List-ID: On Sun, Jul 29, 2007 at 08:56:54PM -0700, Linus Torvalds wrote: > > > On Sun, 29 Jul 2007, Linus Torvalds wrote: > > > > I'd love to hear "here's a real-life load, and yes, the ZERO_PAGE logic > > really does hurt more than it helps, it's time to remove it". At that > > point I'll happily apply the patch. > > Btw, in the absense of that, I'd at least like to hear an acknowledgement > that the complexity isn't worth it, and that what used to work fine was > broken because the reference counting overhead gets us on large-scale > machines. > > IOW, I certainly like removing lines of code. In that sense I _love_ that > patch. I really just react negatively because I really think you first set > ZERO_PAGE up to fail. > > So even if you cannot find a load where this all matters, at least point > to commit b5810039a54e5babf428e9a1e89fc1940fabff11 (or exactly whichever > one it was that started ref-counting ZERO_PAGE) and blame *that* one, > rather than blaming ZERO_PAGE for the problem. OK, as a patch, the changelog could be improved. But I state that complexity isn't worth it as "ZERO_PAGE appears to be a false optimisation". > It has served us well for fifteen years, we shouldn't blame it for > problems that came from elsewhere. Can it still serve us well, though? This is what I would really like to talk about, and I guess would decide whether we again special case the refcounting or remove it completely. I'm happy to do either (although I do *hope* that it can be removed, for complexity's sake). -- 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