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=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 CF0A8C4361B for ; Tue, 15 Dec 2020 03:06:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 89972224D2 for ; Tue, 15 Dec 2020 03:06:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726950AbgLODFz (ORCPT ); Mon, 14 Dec 2020 22:05:55 -0500 Received: from mail.kernel.org ([198.145.29.99]:33318 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726807AbgLODFY (ORCPT ); Mon, 14 Dec 2020 22:05:24 -0500 Date: Mon, 14 Dec 2020 19:04:40 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1608001481; bh=Lcejxg07La87YGD7cY87cJaoDZUtYs9xhkdjBfn9mFs=; h=From:To:Subject:In-Reply-To:From; b=wd7kllceGrp4ykUrbibGhqNx5iIA7QMTaxFmszTu/gkzXJO0JNJhV6CW8zXkOjyfK S8Df2Xp3SWugKGSIonAv3b0ncuVhWo4IyaDHM7/m1yksWO/qnEA8tn5N3L5z59LdK4 Jat0l8ghhg2QEYgAWv0ue0CaRWF2csPU2fX1iUIY= From: Andrew Morton To: akpm@linux-foundation.org, aneesh.kumar@linux.ibm.com, bharata@linux.ibm.com, cl@linux.com, guro@fb.com, hannes@cmpxchg.org, iamjoonsoo.kim@lge.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, rientjes@google.com, shakeelb@google.com, torvalds@linux-foundation.org, vbabka@suse.cz Subject: [patch 024/200] mm/slub: let number of online CPUs determine the slub page order Message-ID: <20201215030440.j0ZgYOoZY%akpm@linux-foundation.org> In-Reply-To: <20201214190237.a17b70ae14f129e2dca3d204@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Bharata B Rao Subject: mm/slub: let number of online CPUs determine the slub page order The page order of the slab that gets chosen for a given slab cache depends on the number of objects that can be fit in the slab while meeting other requirements. We start with a value of minimum objects based on nr_cpu_ids that is driven by possible number of CPUs and hence could be higher than the actual number of CPUs present in the system. This leads to calculate_order() chosing a page order that is on the higher side leading to increased slab memory consumption on systems that have bigger page sizes. Hence rely on the number of online CPUs when determining the mininum objects, thereby increasing the chances of chosing a lower conservative page order for the slab. Vlastimil: : Ideally, we would react to hotplug events and update existing caches : accordingly. But for that, recalculation of order for existing caches : would have to be made safe, while not affecting hot paths. We have : removed the sysfs interface with 32a6f409b693 ("mm, slub: remove runtime : allocation order changes") as it didn't seem easy and worth the trouble. : : In case somebody wants to start with a large order right from the boot : because they know they will hotplug lots of cpus later, they can use : slub_min_objects= boot param to override this heuristic. So in case this : change regresses somebody's performance, there's a way around it and : thus the risk is low IMHO. Link: https://lkml.kernel.org/r/20201118082759.1413056-1-bharata@linux.ibm.com Signed-off-by: Bharata B Rao Acked-by: Vlastimil Babka Acked-by: Roman Gushchin Acked-by: David Rientjes Cc: Christoph Lameter Cc: Joonsoo Kim Cc: Shakeel Butt Cc: Johannes Weiner Cc: Aneesh Kumar K.V Signed-off-by: Andrew Morton --- mm/slub.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/slub.c~mm-slub-let-number-of-online-cpus-determine-the-slub-page-order +++ a/mm/slub.c @@ -3431,7 +3431,7 @@ static inline int calculate_order(unsign */ min_objects = slub_min_objects; if (!min_objects) - min_objects = 4 * (fls(nr_cpu_ids) + 1); + min_objects = 4 * (fls(num_online_cpus()) + 1); max_objects = order_objects(slub_max_order, size); min_objects = min(min_objects, max_objects); _