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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 15BC2C433EF for ; Thu, 31 Mar 2022 07:46:56 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 812698D0001; Thu, 31 Mar 2022 03:46:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7C1476B0073; Thu, 31 Mar 2022 03:46:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6B0FE8D0001; Thu, 31 Mar 2022 03:46:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.hostedemail.com [64.99.140.28]) by kanga.kvack.org (Postfix) with ESMTP id 5F74B6B0072 for ; Thu, 31 Mar 2022 03:46:56 -0400 (EDT) Received: from smtpin08.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 1E0F6244D0 for ; Thu, 31 Mar 2022 07:46:56 +0000 (UTC) X-FDA: 79303900032.08.64D93BD Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by imf10.hostedemail.com (Postfix) with ESMTP id 78677C001C for ; Thu, 31 Mar 2022 07:46:55 +0000 (UTC) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id F318121900; Thu, 31 Mar 2022 07:46:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1648712814; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=MClpEQCEqNuvlVug+pSR2PKBVfdIgjYBgqwIpn2O7Gg=; b=EiSTzvcBcwyt5d21/dSJyyFfU8OvvcT2KgT0DDTSOTwqTFtPB+VgnitdY9jIyVhlxRCI/d AjKiThObJcEEVZ+GMmERBez8Z0qd3Dpkk5E71Z/UOTV+ZekG/Qm4Sl9Gz+agwV55lcHM37 bKv4SA1mfRBLGqhkjuf7XJwdK1aZ9KY= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 52242A3B82; Thu, 31 Mar 2022 07:46:48 +0000 (UTC) Date: Thu, 31 Mar 2022 09:46:52 +0200 From: Michal Hocko To: Shakeel Butt Cc: Roman Gushchin , Andrew Morton , Waiman Long , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Muchun Song Subject: Re: [PATCH v2] mm/list_lru: Fix possible race in memcg_reparent_list_lru_node() Message-ID: References: <20220330191440.1cc1b2de2b849d1ba93d2ba7@linux-foundation.org> <89B53D3A-FCC5-4107-8D49-81D5B9AE5172@linux.dev> <20220331063956.5uqnab64cqnmcwyr@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220331063956.5uqnab64cqnmcwyr@google.com> Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=EiSTzvcB; spf=pass (imf10.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.28 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com X-Stat-Signature: 8jxd6jqqwfqhjj9q1iu6dqjmdk1hiti8 X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 78677C001C X-HE-Tag: 1648712815-222861 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu 31-03-22 06:39:56, Shakeel Butt wrote: > On Wed, Mar 30, 2022 at 07:48:45PM -0700, Roman Gushchin wrote: > > > > > [...] > > > > > > But honestly, I’d drop the original optimization together with > > the fix, if only there is no _real world_ data on the problem and > > the improvement. It seems like it has started as a nice simple > > improvement, but the race makes it complex and probably not worth > > the added complexity and fragility. > > I agree with dropping the original optimization as it is not really > fixing an observed issue which may justify adding some complexity. Completely agreed. The patch as it is proposed is not really acceptable IMHO and I have to say I am worried that this is not the first time we are in a situation when a follow up fixes or unrelated patches are growing in complexity to fit on top of a performance optimizations which do not refer to any actual numbers. -- Michal Hocko SUSE Labs