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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 355A1C433B4 for ; Thu, 8 Apr 2021 17:42:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DBEDC61108 for ; Thu, 8 Apr 2021 17:42:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232377AbhDHRm7 (ORCPT ); Thu, 8 Apr 2021 13:42:59 -0400 Received: from outbound-smtp11.blacknight.com ([46.22.139.106]:41157 "EHLO outbound-smtp11.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231716AbhDHRm6 (ORCPT ); Thu, 8 Apr 2021 13:42:58 -0400 Received: from mail.blacknight.com (pemlinmail06.blacknight.ie [81.17.255.152]) by outbound-smtp11.blacknight.com (Postfix) with ESMTPS id 29DC31C3519 for ; Thu, 8 Apr 2021 18:42:46 +0100 (IST) Received: (qmail 18330 invoked from network); 8 Apr 2021 17:42:45 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.22.4]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 8 Apr 2021 17:42:45 -0000 Date: Thu, 8 Apr 2021 18:42:44 +0100 From: Mel Gorman To: Peter Zijlstra Cc: Linux-MM , Linux-RT-Users , LKML , Chuck Lever , Jesper Dangaard Brouer , Matthew Wilcox , Thomas Gleixner , Ingo Molnar , Michal Hocko , Oscar Salvador Subject: Re: [PATCH 02/11] mm/page_alloc: Convert per-cpu list protection to local_lock Message-ID: <20210408174244.GG3697@techsingularity.net> References: <20210407202423.16022-1-mgorman@techsingularity.net> <20210407202423.16022-3-mgorman@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On Thu, Apr 08, 2021 at 12:52:07PM +0200, Peter Zijlstra wrote: > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index a68bacddcae0..e9e60d1a85d4 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -112,6 +112,13 @@ typedef int __bitwise fpi_t; > > static DEFINE_MUTEX(pcp_batch_high_lock); > > #define MIN_PERCPU_PAGELIST_FRACTION (8) > > > > +struct pagesets { > > + local_lock_t lock; > > +}; > > +static DEFINE_PER_CPU(struct pagesets, pagesets) = { > > + .lock = INIT_LOCAL_LOCK(lock), > > +}; > > So why isn't the local_lock_t in struct per_cpu_pages ? That seems to be > the actual object that is protected by it and is already per-cpu. > > Is that because you want to avoid the duplication across zones? Is that > worth the effort? When I wrote the patch, the problem was that zone_pcp_reset freed the per_cpu_pages structure and it was "protected" by local_irq_save(). If that was converted to local_lock_irq then the structure containing the lock is freed before it is released which is obviously bad. Much later when trying to make the allocator RT-safe in general, I realised that locking was broken and fixed it in patch 3 of this series. With that, the local_lock could potentially be embedded within per_cpu_pages safely at the end of this series. -- Mel Gorman SUSE Labs