Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759771AbcLVT2l (ORCPT ); Thu, 22 Dec 2016 14:28:41 -0500 Received: from mail-pg0-f45.google.com ([74.125.83.45]:33656 "EHLO mail-pg0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757307AbcLVT2k (ORCPT ); Thu, 22 Dec 2016 14:28:40 -0500 Date: Thu, 22 Dec 2016 11:28:31 -0800 (PST) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Linus Torvalds cc: Peter Zijlstra , Nick Piggin , Dave Hansen , Bob Peterson , Linux Kernel Mailing List , Steven Whitehouse , Andrew Lutomirski , Andreas Gruenbacher , Mel Gorman , linux-mm Subject: Re: [RFC][PATCH] make global bitlock waitqueues per-node In-Reply-To: Message-ID: References: <20161219225826.F8CB356F@viggo.jf.intel.com> <156a5b34-ad3b-d0aa-83c9-109b366c1bdf@linux.intel.com> <20161221080931.GQ3124@twins.programming.kicks-ass.net> <20161221083247.GW3174@twins.programming.kicks-ass.net> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1857 Lines: 45 On Wed, 21 Dec 2016, Linus Torvalds wrote: > On Wed, Dec 21, 2016 at 12:32 AM, Peter Zijlstra wrote: > > > > FWIW, here's mine.. compiles and boots on a NUMA x86_64 machine. > > So I like how your patch is smaller, but your patch is also broken. > > First off, the whole contention bit is *not* NUMA-specific. It should > help non-NUMA too, by avoiding the stupid extra cache miss. > > Secondly, CONFIG_NUMA is a broken thing to test anyway, since adding a > bit for the NUMA case can overflow the page flags as far as I can tell > (MIPS seems to support NUMA on 32-bit, for example, but I didn't > really check the Kconfig details). Making it dependent on 64-bit might > be ok (and would fix the issue above - I don't think we really need to > care too much about 32-bit any more) > > But making it conditional at all means that now you have those two > different cases for this, which is a maintenance nightmare. So don't > do it even if we could say "screw 32-bit". > > Anyway, the conditional thing could be fixed by just taking Nick's > patch 1/2, and your patch (with the conditional bits stripped out). Yup. > > I do think your approach of just re-using the existing bit waiting > with just a page-specific waiting function is nicer than Nick's "let's > just roll new waiting functions" approach. It also avoids the extra > initcall. > > Nick, comments? > > Hugh - mind testing PeterZ's patch too? My comments about the > conditional PG_waiters bit and page bit overflow are not relevant for > your particular scenario, so you can ignore that part, and just take > PaterZ's patch directly. Right, I put them both through some loads yesterday and overnight: Peter's patch and Nick's patch each work fine here, no issues seen with either (but I didn't attempt to compare them, aesthetically nor in performance). Hugh