From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f69.google.com (mail-pa0-f69.google.com [209.85.220.69]) by kanga.kvack.org (Postfix) with ESMTP id 7C1016B0253 for ; Thu, 29 Sep 2016 09:16:58 -0400 (EDT) Received: by mail-pa0-f69.google.com with SMTP id bv10so139854189pad.2 for ; Thu, 29 Sep 2016 06:16:58 -0700 (PDT) Received: from bombadil.infradead.org (bombadil.infradead.org. [2001:1868:205::9]) by mx.google.com with ESMTPS id s86si14410963pfd.23.2016.09.29.06.16.57 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 29 Sep 2016 06:16:57 -0700 (PDT) Date: Thu, 29 Sep 2016 15:16:35 +0200 From: Peter Zijlstra Subject: Re: page_waitqueue() considered harmful Message-ID: <20160929131635.GY5016@twins.programming.kicks-ass.net> References: <20160927073055.GM2794@worktop> <20160927085412.GD2838@techsingularity.net> <20160929080130.GJ3318@worktop.controleur.wifipass.org> <20160929225544.70a23dac@roar.ozlabs.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160929225544.70a23dac@roar.ozlabs.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Nicholas Piggin Cc: Mel Gorman , Linus Torvalds , Andrew Morton , "Kirill A. Shutemov" , Johannes Weiner , Jan Kara , Rik van Riel , linux-mm On Thu, Sep 29, 2016 at 10:55:44PM +1000, Nicholas Piggin wrote: > On Thu, 29 Sep 2016 10:01:30 +0200 > Peter Zijlstra wrote: > > > On Tue, Sep 27, 2016 at 09:54:12AM +0100, Mel Gorman wrote: > > > On Tue, Sep 27, 2016 at 09:30:55AM +0200, Peter Zijlstra wrote: > > > Simple is relative unless I drastically overcomplicated things and it > > > wouldn't be the first time. 64-bit only side-steps the page flag issue > > > as long as we can live with that. > > > > So one problem with the 64bit only pageflags is that they do eat space > > from page-flags-layout, we do try and fit a bunch of other crap in > > there, and at some point that all will not fit anymore and we'll revert > > to worse. > > > > I've no idea how far away from that we are for distro kernels. I suppose > > they have fairly large NR_NODES and NR_CPUS. > > I know it's not fashionable to care about them anymore, but it's sad if > 32-bit architectures miss out fundamental optimisations like this because > we're out of page flags. It would also be sad to increase the size of > struct page because we're too lazy to reduce flags. There's some that > might be able to be removed. I'm all for cleaning some of that up, but its been a long while since I poked in that general area. -- 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