From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-1.1 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FROM,MAILING_LIST_MULTI,RCVD_IN_DNSWL_NONE autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 22787 invoked from network); 5 Feb 2021 18:22:29 -0000 Received: from minnie.tuhs.org (45.79.103.53) by inbox.vuxu.org with ESMTPUTF8; 5 Feb 2021 18:22:29 -0000 Received: by minnie.tuhs.org (Postfix, from userid 112) id 386BF9C2E4; Sat, 6 Feb 2021 04:22:27 +1000 (AEST) Received: from minnie.tuhs.org (localhost [127.0.0.1]) by minnie.tuhs.org (Postfix) with ESMTP id B36699BA45; Sat, 6 Feb 2021 04:22:08 +1000 (AEST) Authentication-Results: minnie.tuhs.org; dkim=pass (2048-bit key; unprotected) header.d=gmail.com header.i=@gmail.com header.b="AzxGDj/K"; dkim-atps=neutral Received: by minnie.tuhs.org (Postfix, from userid 112) id B30199BA45; Sat, 6 Feb 2021 04:22:06 +1000 (AEST) Received: from mail-ot1-f45.google.com (mail-ot1-f45.google.com [209.85.210.45]) by minnie.tuhs.org (Postfix) with ESMTPS id 190029BA3F for ; Sat, 6 Feb 2021 04:22:06 +1000 (AEST) Received: by mail-ot1-f45.google.com with SMTP id o12so7739222ote.12 for ; Fri, 05 Feb 2021 10:22:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=stqR35ssFlOu+pCqGFol5/gt6P9VdG8YkGzJtmXxo8A=; b=AzxGDj/KyKD/t/zrm7JBV+XUTGybY4GokdWUR+55yEuRdIVcB/Mom+vUtIOF1aQHEC caPw067VIfI3YMiop+j2WLHI3Fh+Vq38db0QTDrpjPvR3+szHwrSxSrZ5MoxReXtsjvU PJdM86gsbw1WnIV6l76ib14UvE8Sg5f53gSQforhpgLN814gZcBlkHnY91CXsNzrMZWS Mv0kUJVFvYPisOHE770ERLzJzKs7Jk+KavZjsqZSJagePyMNz2hW6/D2XPazYAKWtT1r 3laEBXSGb9WssRgihcSg1C5fnA3Iz4tPBteyWsXR7xD5a2yjOCppOleD0vysx+8ShT+x LagQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=stqR35ssFlOu+pCqGFol5/gt6P9VdG8YkGzJtmXxo8A=; b=M0ToDmlSeY4hsboTfrL5HXs2y303FC1pOQ2qj4RG619NA06ddpL7LdGJttLaLDt2zT cpyYr0YydVyeutvvKPpc+Gw9XCh6j9zlDSTob/QSskmehWLEm0tkM6n/WAT1zYCv9bJW gbUa/txPVpSLygwjLrN3XEujFOuxHdavpjjvbAD/tg7zXJ1equresv0KhXd//F+b7gj3 nVK6ZuL1zh2NjrNfIsr7Rw7qJqHsDbSp7H3mtNoJDyvi0QUtKK1vzJcIAdIBq8+L57Yi lavyQOB1qwwlqa2ax8YxwgytwymJSy2xK7/bhOCgLWCCDMicRzM538uDBxuhwtdoGKwR xCnw== X-Gm-Message-State: AOAM530xE9sDXpg/1Kp9y2s/pCZkWUXD7fYaB9OtBrb6DFzw5HfUICo7 uRVRwgOhizaEWYkr2lRyWvj3vfsGHe1+B01t+uc= X-Google-Smtp-Source: ABdhPJyuKXpzI77JfCn84W5mqh1S2IrVFt513pdWXk7++DGPY/2e57Py+a2DV+BeiDQTHzmIVaTP8bICQAEkUVy0ibw= X-Received: by 2002:a9d:1ee2:: with SMTP id n89mr4321109otn.6.1612549325441; Fri, 05 Feb 2021 10:22:05 -0800 (PST) MIME-Version: 1.0 References: <20210205003315.GK13701@mcvoy.com> <26D923CF-5319-4207-BA28-6EFA0E3BB1F8@iitbombay.org> <20210205141820.GO13701@mcvoy.com> In-Reply-To: <20210205141820.GO13701@mcvoy.com> From: ron minnich Date: Fri, 5 Feb 2021 10:21:54 -0800 Message-ID: To: Larry McVoy Content-Type: text/plain; charset="UTF-8" Subject: Re: [TUHS] FreeBSD behind the times? (was: Favorite unix design principles?) X-BeenThere: tuhs@minnie.tuhs.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: The Unix Heritage Society mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Bakul Shah , TUHS main list Errors-To: tuhs-bounces@minnie.tuhs.org Sender: "TUHS" I think hearing *why* they did that would be interesting. On Fri, Feb 5, 2021 at 6:19 AM Larry McVoy wrote: > > On Thu, Feb 04, 2021 at 09:17:54PM -0800, Bakul Shah wrote: > > On Feb 4, 2021, at 4:33 PM, Larry McVoy wrote: > > > > > > Ignoring the page cache and make their own cache has big problems. > > > You can mmap() ZFS files and doing so means that when a page is referenced > > > it is copied from the ZFS cache to the page cache. That creates a > > > coherency problem, I can write via the mapping and I can write via > > > write(2) and now you have two copies of the data that don't match, > > > that's pretty much OS no-no #1. > > > > Write(2)ing to a mapped page sounds pretty dodgy. Likely to get you > > in trouble in any case. Similarly read(2)ing. > > The entire point of the SunOS 4.0 VM system was that the page you > saw via mmap(2) is the exact same page you saw via read(2). It's > the page cache, it has page sized chunks of memory that cache > file,offset pairs. > > There is one, and only one, copy of the truth. Doesn't matter how > you get at it, there is only one "it". > > ZFS broke that contract and that was a step backwards in terms of > OS design.