From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D0029C282C2 for ; Wed, 13 Feb 2019 19:17:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A797121904 for ; Wed, 13 Feb 2019 19:17:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388700AbfBMTRK (ORCPT ); Wed, 13 Feb 2019 14:17:10 -0500 Received: from outbound-smtp25.blacknight.com ([81.17.249.193]:50991 "EHLO outbound-smtp25.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727053AbfBMTRJ (ORCPT ); Wed, 13 Feb 2019 14:17:09 -0500 Received: from mail.blacknight.com (pemlinmail04.blacknight.ie [81.17.254.17]) by outbound-smtp25.blacknight.com (Postfix) with ESMTPS id AC1E1B8719 for ; Wed, 13 Feb 2019 19:17:07 +0000 (GMT) Received: (qmail 3371 invoked from network); 13 Feb 2019 19:17:07 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[37.228.225.79]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 13 Feb 2019 19:17:07 -0000 Date: Wed, 13 Feb 2019 19:17:06 +0000 From: Mel Gorman To: Peter Zijlstra Cc: Alexander Shishkin , Arnaldo Carvalho de Melo , Ingo Molnar , linux-kernel@vger.kernel.org, jolsa@redhat.com Subject: Re: [PATCH v0 1/2] perf: Add an option to ask for high order allocations for AUX buffers Message-ID: <20190213191705.GV9565@techsingularity.net> References: <20190213114716.63972-1-alexander.shishkin@linux.intel.com> <20190213114716.63972-2-alexander.shishkin@linux.intel.com> <20190213130755.GQ32494@hirez.programming.kicks-ass.net> <20190213174756.GU9565@techsingularity.net> <20190213175434.GA32494@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20190213175434.GA32494@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 13, 2019 at 06:54:34PM +0100, Peter Zijlstra wrote: > On Wed, Feb 13, 2019 at 05:47:56PM +0000, Mel Gorman wrote: > > If there is a tangiable performance benefit from using contiguous regions > > then I would suggest optimistically allocating them with appropriate > > GFP flags to avoid large latencies at startup time and fall back if > > necessary. > > Right; the code does the fallback thing. It successively tries smaller > order allocations until 0-order fails. > > It currently uses: > > #define PERF_AUX_GFP (GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN | __GFP_NORETRY) > > Is that what you could consider appropriate? Yeah, spot on. Conceivably the semantics of __GFP_NORETY will change a little at some point in the next year but not in any way I'd consider harmful (depends on how THP and locality discussions go). Even *if* we did something harmful, there will be complaints before it's problematic. -- Mel Gorman SUSE Labs