From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f70.google.com (mail-pa0-f70.google.com [209.85.220.70]) by kanga.kvack.org (Postfix) with ESMTP id 76B9E280251 for ; Thu, 29 Sep 2016 03:15:00 -0400 (EDT) Received: by mail-pa0-f70.google.com with SMTP id fu14so126407994pad.0 for ; Thu, 29 Sep 2016 00:15:00 -0700 (PDT) Received: from bombadil.infradead.org (bombadil.infradead.org. [2001:1868:205::9]) by mx.google.com with ESMTPS id y5si2438520pfk.271.2016.09.29.00.14.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 29 Sep 2016 00:14:59 -0700 (PDT) Date: Thu, 29 Sep 2016 09:14:51 +0200 From: Peter Zijlstra Subject: Re: page_waitqueue() considered harmful Message-ID: <20160929071451.GI3318@worktop.controleur.wifipass.org> References: <20160927083104.GC2838@techsingularity.net> <20160928005318.2f474a70@roar.ozlabs.ibm.com> <20160927165221.GP5016@twins.programming.kicks-ass.net> <20160928030621.579ece3a@roar.ozlabs.ibm.com> <20160928070546.GT2794@worktop> <20160929113132.5a85b887@roar.ozlabs.ibm.com> <20160929062132.GG3318@worktop.controleur.wifipass.org> <20160929164231.166d2910@roar.ozlabs.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160929164231.166d2910@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 , Will Deacon , Paul McKenney , Alan Stern On Thu, Sep 29, 2016 at 04:42:31PM +1000, Nicholas Piggin wrote: > Take Alpha instead. It's using 32-bit ops. Hmm, my Alpha docs are on the other machine, but I suppose the problem is 64bit immediates (which would be a common problem I suppose, those don't really work well on x86 either). Yes, that does make it all more tricky than desired. OTOH maybe this is a good excuse to (finally) sanitize the bitmap API to use a fixed width. It using 'unsigned long' has been something of a pain at times. With that it would be 'obvious' bits need to be part of the same 32bit word and we can use the normal smp_mb__{before,after}_atomic() again. Given our bitops really are only about single bits, I can't see the change making a real performance difference. OTOH, the non atomic things like weight and ff[sz] do benefit from using the longer words. Bother.. -- 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