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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 3DAC7C04E83 for ; Tue, 21 Aug 2018 05:11:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E44C521735 for ; Tue, 21 Aug 2018 05:11:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="rbD6F7at" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E44C521735 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726789AbeHUIaT (ORCPT ); Tue, 21 Aug 2018 04:30:19 -0400 Received: from mail-yb0-f195.google.com ([209.85.213.195]:37101 "EHLO mail-yb0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726628AbeHUIaT (ORCPT ); Tue, 21 Aug 2018 04:30:19 -0400 Received: by mail-yb0-f195.google.com with SMTP id f145-v6so3354773ybg.4 for ; Mon, 20 Aug 2018 22:11:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=u0nxW5SDhuR0cvWLvp9dYb5Hfu9HpYKt5PL/ZEZtZfA=; b=rbD6F7atGDmxMdCk2jaAHJPTfxPhtNeEBlP06bFLTIcEUjnRvJJsZUZrBoUN/4T2WQ wY9OaR0SfPtETJrdjblzyKy3sVv6fTzTWzl3K+3letCz3QPn81b12t81d4mxUE6PhPKm puOQSmPoOFiZqLky3GTNN/OxC6ki3EcNIPXywlh3MEf6JWL+5Ki4TUW9iGI3oHJs58xL WoGgug4SFY4buul5YJzN8kCi483lZqPYOmRM4kW+tGFSv/86eAePkUh1rH5zDyCSVJvE wZsKh7qVhmsJFH/y3Ce+PvBhtQCJigLf3Fu47OWiDOi1r0OgPDQN36OJeJiHEE2bA5Bl fsJw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=u0nxW5SDhuR0cvWLvp9dYb5Hfu9HpYKt5PL/ZEZtZfA=; b=IDzoZIhMe6h+SA1RRHIX5vhN71Ru+FMM0s8Rv8WYgNMHaplz/7PA9EdTyI4uEYHDIq AMsmdS65hvvzdML2Bo/T9YYDPY39hXF2FrfoVZUtk8xtg38ojBdc6Cf34TffOvaB1mP4 mFJHVPYWxhk+DOzrLCOchZHPGL6r96DGJIsXdh/FuBd1TMVtsz6y43jAUA21M/0zbxT6 Pz6D6fpxHqKDV24hI6niIQlqvlWykuw28YiX9hPHNvQisiMl7tDPNkpOcgId/HlNEoWQ cC6SujCKhNPtkbDRH6LM6Phd6qtZUK47+gVc5xicD5OCXIFYjOUFuPV7BvW0gmXmkiNp T4EA== X-Gm-Message-State: AOUpUlFx5mGzOL7Wrc0kIWQe0L6JYdEPtkoRCDW5QAyZsRA1QUiyZNG5 15GTdHE9IX3PiZby+AwER3sRokDAiwxH6WJZUIk= X-Google-Smtp-Source: AA+uWPwoWSMfSEqn3KWfdb6Q5JGYvTX33bvSXrTS8q8VVcigwyVhi8yP9kFHRm47Li98o9sY4lDznsQiPKD+0ox1wUg= X-Received: by 2002:a25:bdcf:: with SMTP id g15-v6mr3711493ybk.494.1534828305596; Mon, 20 Aug 2018 22:11:45 -0700 (PDT) MIME-Version: 1.0 Received: by 2002:a0d:c142:0:0:0:0:0 with HTTP; Mon, 20 Aug 2018 22:11:44 -0700 (PDT) In-Reply-To: <20180818012213.GA14115@bombadil.infradead.org> References: <20180817231834.15959-1-guro@fb.com> <20180818012213.GA14115@bombadil.infradead.org> From: Konstantin Khlebnikov Date: Tue, 21 Aug 2018 08:11:44 +0300 Message-ID: Subject: Re: [PATCH RFC] mm: don't miss the last page because of round-off error To: Matthew Wilcox Cc: Roman Gushchin , linux-mm@kvack.org, Linux Kernel Mailing List , kernel-team@fb.com, Andrew Morton , Johannes Weiner , Michal Hocko , Tejun Heo , Rik van Riel Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Aug 18, 2018 at 4:22 AM, Matthew Wilcox wrote: > On Fri, Aug 17, 2018 at 04:18:34PM -0700, Roman Gushchin wrote: >> - scan = div64_u64(scan * fraction[file], >> - denominator); >> + if (scan > 1) >> + scan = div64_u64(scan * fraction[file], >> + denominator); > > Wouldn't we be better off doing a div_round_up? ie: > > scan = div64_u64(scan * fraction[file] + denominator - 1, denominator); > > although i'd rather hide that in a new macro in math64.h than opencode it > here. All numbers here should be up to nr_pages * 200 and fit into unsigned long. I see no reason for u64. If they overflow then u64 wouldn't help either. There is macro DIV_ROUND_UP in kernel.h