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=-2.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 43734C3A59F for ; Mon, 26 Aug 2019 12:27:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 135FD20874 for ; Mon, 26 Aug 2019 12:27:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="dg+K9npC" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731522AbfHZM1V (ORCPT ); Mon, 26 Aug 2019 08:27:21 -0400 Received: from mail-io1-f67.google.com ([209.85.166.67]:43878 "EHLO mail-io1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726269AbfHZM1V (ORCPT ); Mon, 26 Aug 2019 08:27:21 -0400 Received: by mail-io1-f67.google.com with SMTP id 18so36702736ioe.10 for ; Mon, 26 Aug 2019 05:27:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=H/N7gWnruTlKacQqDAeFeHHNleOd/fi/7ZUbFS509DU=; b=dg+K9npC21k+XHEVWnp4AFoQFOCYEE88YbGoektA/QEQi11Gi9pib16sHnHXz5izrA 8CTd9xPxImD33vvaGGIwlH0TaRjZjeBTBBrp9TkCC2THNSQIIZDoOFTtSSZ9KDWCx/w0 78wAdrVF3N2WTylLkUa19V4XjoZkS01ubXRWyH1+JlMKflU+TyfizLh6fOJqB/b64SlK 1/eHYnfD1u9Cqc/6e1eU32fnyHkXbFsf74IcBlbNMK3DzDtGXO9hAPYuI1ZVw4mrGI+n ke3vz+YdEek2RDsGo7mB87gGGdeMGPcAWrmUDxNeLRoEuegmPDpPsungjkZxM67/UTDi hMZw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=H/N7gWnruTlKacQqDAeFeHHNleOd/fi/7ZUbFS509DU=; b=gAWLXNKaMYbtG0XJP+pxrwDpVbDJtmgBC4KSDfFqts0qnFE5JHy+QZSei7SP21WSug 5vrXucd3b41s3oCR+2Owyic3SFTbwHHCP8m4sn++gS0WKudVFdskDcDN+uQXuzLaOWiD K7SoMZEdNTbvwR2phXuQl2kx2NZrJesXRLKrg0pWICLTI1TaRX2PL+cfS3P7D7Z4fYU+ cSdi8fP/LU85XLBUKX88LzOw9316vfa71rb0ZTWKaqzCtoB4qLClpUM8i8A7J74skJml H6gKJDr19+VL/4dF5elSHN/vdrhNwGIGVfngGKfwvRokdXypsjdAEvEc/o6ylRqfQgy5 zueg== X-Gm-Message-State: APjAAAXx+G5kFbBnvIV8L9qyuGosP0EHgzeQfUnoZQHso+nyb61wN6Wx bm1vItzErEsnibq//X3db3ByyO0Utn4= X-Google-Smtp-Source: APXvYqxn/7GGBOUv35hVcPEYef/6tITopBTZXmwyf0/RViVMvHuKQOhm0zBDZ+2KrEdDg5UQURY0VQ== X-Received: by 2002:a05:6638:1e5:: with SMTP id t5mr17836081jaq.79.1566822439877; Mon, 26 Aug 2019 05:27:19 -0700 (PDT) Received: from [191.9.209.46] (rrcs-70-62-41-24.central.biz.rr.com. [70.62.41.24]) by smtp.gmail.com with ESMTPSA id s12sm10552557ios.31.2019.08.26.05.27.18 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 26 Aug 2019 05:27:19 -0700 (PDT) Subject: Re: [PATCH v2 0/4] Support xxhash64 checksums To: Adam Borowski , Paul Jones Cc: Peter Becker , =?UTF-8?Q?Holger_Hoffst=c3=a4tte?= , Linux BTRFS Mailinglist References: <20190822114029.11225-1-jthumshirn@suse.de> <20190823170845.GD17075@angband.pl> From: "Austin S. Hemmelgarn" Message-ID: <69ac4340-c782-aa92-246c-3106b1611eea@gmail.com> Date: Mon, 26 Aug 2019 08:27:15 -0400 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190823170845.GD17075@angband.pl> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 2019-08-23 13:08, Adam Borowski wrote: > the improved collision > resistance of xxhash64 is not a reason as if you intend to dedupe you want > a crypto hash so you don't need to verify. The improved collision resistance is a roughly 10 orders of magnitude reduction in the chance of a collision. That may not matter for most, but it's a significant improvement for anybody operating at large enough scale that media errors are commonplace. Also, you would still need to verify even if you're using whatever the fanciest new collision resistant cryptographic hash is, because the number of possible input values is still more than _nine thousand_ orders of magnitude larger than the total number of output values even if we use a 512-bit cryptographic hash.