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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 264C1C433EF for ; Tue, 12 Oct 2021 11:38:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 050CA61074 for ; Tue, 12 Oct 2021 11:38:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236297AbhJLLkL (ORCPT ); Tue, 12 Oct 2021 07:40:11 -0400 Received: from outbound-smtp53.blacknight.com ([46.22.136.237]:34479 "EHLO outbound-smtp53.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236289AbhJLLkJ (ORCPT ); Tue, 12 Oct 2021 07:40:09 -0400 Received: from mail.blacknight.com (pemlinmail01.blacknight.ie [81.17.254.10]) by outbound-smtp53.blacknight.com (Postfix) with ESMTPS id 3314AFAB37 for ; Tue, 12 Oct 2021 12:38:06 +0100 (IST) Received: (qmail 17393 invoked from network); 12 Oct 2021 11:38:06 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.17.29]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 12 Oct 2021 11:38:05 -0000 Date: Tue, 12 Oct 2021 12:38:04 +0100 From: Mel Gorman To: Vasily Averin Cc: Vlastimil Babka , Michal Hocko , Johannes Weiner , Vladimir Davydov , Andrew Morton , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel@openvz.org, Uladzislau Rezki Subject: Re: [PATCH memcg] mm/page_alloc.c: avoid statistic update with 0 Message-ID: <20211012113804.GT3959@techsingularity.net> References: <29155011-f884-b0e5-218e-911039568acb@suse.cz> 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-kernel@vger.kernel.org On Tue, Oct 12, 2021 at 01:42:41PM +0300, Vasily Averin wrote: > On 08.10.2021 14:47, Vlastimil Babka wrote: > > On 10/8/21 11:24, Vasily Averin wrote: > >> __alloc_pages_bulk can call __count_zid_vm_events and zone_statistics > >> with nr_account = 0. > > > > But that's not a bug, right? Just an effective no-op that's not commonly > > happening, so is it worth the check? > > Why not? > > Yes, it's not a bug, it just makes the kernel a bit more efficient in a very unlikely case. At the cost of an additional branch in the likely case that may be mispredicted. > However, it looks strange and makes uninformed code reviewers like me worry about possible > problems inside the affected functions. No one else calls these functions from 0. > The accounting functions should still work with a 0 delta. -- Mel Gorman SUSE Labs