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=-3.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS autolearn=no 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 C0E82C4332E for ; Fri, 20 Mar 2020 15:55:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8D88920767 for ; Fri, 20 Mar 2020 15:55:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=cmpxchg-org.20150623.gappssmtp.com header.i=@cmpxchg-org.20150623.gappssmtp.com header.b="h9BpRW81" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727297AbgCTPzJ (ORCPT ); Fri, 20 Mar 2020 11:55:09 -0400 Received: from mail-qv1-f65.google.com ([209.85.219.65]:44034 "EHLO mail-qv1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726144AbgCTPzJ (ORCPT ); Fri, 20 Mar 2020 11:55:09 -0400 Received: by mail-qv1-f65.google.com with SMTP id w5so3186952qvp.11 for ; Fri, 20 Mar 2020 08:55:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cmpxchg-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=kA54VswZsT5/CNlwIwZBY/H30VVL/ablHOI+ykDEfUw=; b=h9BpRW81+Xm0pLBVCmKH2IdQD4VSOMFNFWYiZwvPVdobwa/P6HtGQIJtQXZJXU5CLz qStLK2ZD5vaYWKNyFsI+0O7m7raDmTcfNQd55TxjcluITF+TqXPXWxIhrfuLMEASvnf1 AWwe3LDrYTmqVPTDdtP3tKgwpar+TRSFwjRRXqBxfWp62gXvUBPt/nWvu9lPQhjOnOMt XDxekKzMPuj3xlrxEWmTLZIh3ki9YqmWRQWZZS3ILij5BEMMD4iArLkNYJPGq1hz3gr3 YKJvqGki+efSkGuckkUDGK2qUr6vAI8G0OS72Xb530svwx80KSuJ4t1fAcZ6bsIDySzO TmGQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=kA54VswZsT5/CNlwIwZBY/H30VVL/ablHOI+ykDEfUw=; b=O5ewxSzbO6gdZfuw3CoUpyAHA0TmDwMR+YyKj5ZRBuAWcfBj940T905/UsirdW4wyM HQH6R5frnnMsIQdpATuhB7qMvfmgz8vXcpXM0ucW7ov4f89kvS7Rk3XHy28uOU3XU31d WIOG8ypEK+nBadapCqdQzaCxVTrDQ9/fGqfY6ip0fSf+1AS7vmHkpIVs0Rc09+fxMZ1r 6fIK+ZQZEDICXQNlMcykkVKPlwkotmkZVrznfW7CZ4jbRB9n/ezZQ8VoQw29GrsKYMmb Q2lMG19RgUFZQ76h8naK5g1vwEObijw7gpFMeLrTHTk997a1zUuRKj8m9PxqNvraErNu v4Nw== X-Gm-Message-State: ANhLgQ0cCKtgXAg7duEjBYPNCtqkwLqsspthJduzVdQvep5nbeEQTmw6 mvZtTaQtAe98hXntqMsuyg48W5evgqw= X-Google-Smtp-Source: ADFU+vveo0N4CHbisUB5ArxqhCh+Kdu2UDfHtyEOWTY+K6g/iOG43vJUwa4Ie5ooLXrDSnkymo6JZw== X-Received: by 2002:a0c:d601:: with SMTP id c1mr4222390qvj.164.1584719707712; Fri, 20 Mar 2020 08:55:07 -0700 (PDT) Received: from localhost ([2620:10d:c091:480::1:a9a9]) by smtp.gmail.com with ESMTPSA id c40sm5218215qtk.18.2020.03.20.08.55.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Mar 2020 08:55:06 -0700 (PDT) Date: Fri, 20 Mar 2020 11:55:05 -0400 From: Johannes Weiner To: Michal Hocko Cc: mateusznosek0@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org Subject: Re: [PATCH] mm/vmscan.c: Clean code by removing unnecessary assignment Message-ID: <20200320155505.GA204561@cmpxchg.org> References: <20200319165938.23354-1-mateusznosek0@gmail.com> <20200319171334.GK20800@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200319171334.GK20800@dhcp22.suse.cz> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 19, 2020 at 06:13:34PM +0100, Michal Hocko wrote: > It is usually preferable to Cc author of the code (added Johannes) > > On Thu 19-03-20 17:59:38, mateusznosek0@gmail.com wrote: > > From: Mateusz Nosek > > > > Previously 0 was assigned to 'sc->skipped_deactivate'. It could happen only > > if 'sc->skipped_deactivate' was 0 so the assignment is unnecessary and can > > be removed. > > The above wording was a bit hard to understdand for me. I would go with > " > sc->memcg_low_skipped resets skipped_deactivate to 0 but this is not > needed as this code path is never reachable with skipped_deactivate != 0 > due to previous sc->skipped_deactivate branch. > " Yeah that sounds good. > > Signed-off-by: Mateusz Nosek > > The patch is correct. I am not sure it results in a better code though. > I will defer to Johannes here. I suspect he simply wanted to express > that skipped_deactivate should be always reset when retrying the direct > reclaim. After this patch this could be lost in future changes so the > code would be more subtle. But I am only guessing here. It's a valid concern, but I think in this case specifically we're very unlikely to change the ordering here - violate memory.low before going after active pages of unprotected cgroups. I indeed just kept it stupid: reset everything, then retry. But it appears that the unnecessary assignment trips people up and wastes their time, so I'm in favor of removing it. Acked-by: Johannes Weiner