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=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 69315C433EF for ; Fri, 24 Sep 2021 01:18:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3E3B761029 for ; Fri, 24 Sep 2021 01:18:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243676AbhIXBT7 (ORCPT ); Thu, 23 Sep 2021 21:19:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55910 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243687AbhIXBT5 (ORCPT ); Thu, 23 Sep 2021 21:19:57 -0400 Received: from mail-pg1-x52f.google.com (mail-pg1-x52f.google.com [IPv6:2607:f8b0:4864:20::52f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DA3B0C061756 for ; Thu, 23 Sep 2021 18:18:24 -0700 (PDT) Received: by mail-pg1-x52f.google.com with SMTP id h3so8211598pgb.7 for ; Thu, 23 Sep 2021 18:18:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20210112.gappssmtp.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=uqQDICrjwFm5U5Uqyn+9fRddYNuzSxkxhD6TsyPwFBQ=; b=uXNOky86fkvBPovVcGHqsg5IwilbsRlOyStj5vunQE+xO6ynctO2vW7os8mbaYjcsR Qp5hu2w3ytkFTB1E96kYCQXeKKJ3znG3ZkZXhKxPcJmAq/pJOGYT4eLzLdtWxcaFsgbW ENUjyG6uPw2J4ZqNP6esg68acUn+YxbaLxSmDL/jo4KGDnDlG/p72+6bTchIVtxSEoYS 3G939lLxpjbhFqWLsYpTB+wxvApDJu6HC8Qb0V/89oJKgy7mYrmnFeQlYNh/jbZRBcmx 4o2f6tfMRYx3/e5QXadun+TOiLIlQt/doA6HhpS9Z8vRIssVMD3+yCeMJAf12WYlmQPg qHjw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=uqQDICrjwFm5U5Uqyn+9fRddYNuzSxkxhD6TsyPwFBQ=; b=5Wg1ybrq0f/ErqoQExCPgotSsygyq4f1ajF0FryB+2oGfLZDjl9PAHur1Hri/vVrEZ 4a0rPOJZglNRWoYMfpSGNg8YiG51S8C7izApBhiedhxlzijARlcPCpud7Zcy0sEmRJho /R7fgJzEuJjErcatwK6HrzXRyok9/xHEoKFTsWV4LxZg/bAh6ln89WwNeAHgbz/ngO9R Az/MrIZLi/iHAOFw9Ocq9YtPwk3JD9p8MqFg8d3wQO2yCq8WvWnycGbzlw84+oWO/UH9 lKHEurKfCR6k1yAE35tCQZ18SekAZJVipxnaVIUfIEFaHWKRAws2zZFExZYgs57+rQ13 kMqg== X-Gm-Message-State: AOAM532EPCpiU1RcYLpdPJldKPtrfM1GVOmmAsEGJXSKiROtq5fjxcIx fpRE4znmQ4LJ7z/1cdGwam+ia345g7kML480CIK8LA== X-Google-Smtp-Source: ABdhPJzx05Y6tsQ2rjQB5YOjhPY8GQyoQfvzyT7OPxy8YpAQmaxyp5sYZSC4GQnhFHY5Xe7WeClQ8/6XBCJBO3iFJx4= X-Received: by 2002:a62:1b92:0:b0:3eb:3f92:724 with SMTP id b140-20020a621b92000000b003eb3f920724mr7477416pfb.3.1632446304295; Thu, 23 Sep 2021 18:18:24 -0700 (PDT) MIME-Version: 1.0 References: <20210922023801.GD570615@magnolia> <20210922035907.GR1756565@dread.disaster.area> <20210922041354.GE570615@magnolia> <20210922054931.GT1756565@dread.disaster.area> <20210922212725.GN570615@magnolia> <20210923000255.GO570615@magnolia> <20210923014209.GW1756565@dread.disaster.area> <20210923225433.GX1756565@dread.disaster.area> In-Reply-To: <20210923225433.GX1756565@dread.disaster.area> From: Dan Williams Date: Thu, 23 Sep 2021 18:18:12 -0700 Message-ID: Subject: Re: [PATCH 3/5] vfs: add a zero-initialization mode to fallocate To: Jane Chu Cc: "Darrick J. Wong" , Christoph Hellwig , linux-xfs , linux-fsdevel , Dave Chinner Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Thu, Sep 23, 2021 at 3:54 PM Dave Chinner wrote: > > On Wed, Sep 22, 2021 at 10:42:11PM -0700, Dan Williams wrote: > > On Wed, Sep 22, 2021 at 7:43 PM Dan Williams wrote: > > > > > > On Wed, Sep 22, 2021 at 6:42 PM Dave Chinner wrote: > > > [..] > > > > Hence this discussion leads me to conclude that fallocate() simply > > > > isn't the right interface to clear storage hardware poison state and > > > > it's much simpler for everyone - kernel and userspace - to provide a > > > > pwritev2(RWF_CLEAR_HWERROR) flag to directly instruct the IO path to > > > > clear hardware error state before issuing this user write to the > > > > hardware. > > > > > > That flag would slot in nicely in dax_iomap_iter() as the gate for > > > whether dax_direct_access() should allow mapping over error ranges, > > > and then as a flag to dax_copy_from_iter() to indicate that it should > > > compare the incoming write to known poison and clear it before > > > proceeding. > > > > > > I like the distinction, because there's a chance the application did > > > not know that the page had experienced data loss and might want the > > > error behavior. The other service the driver could offer with this > > > flag is to do a precise check of the incoming write to make sure it > > > overlaps known poison and then repair the entire page. Repairing whole > > > pages makes for a cleaner implementation of the code that tries to > > > keep poison out of the CPU speculation path, {set,clear}_mce_nospec(). > > > > This flag could also be useful for preadv2() as there is currently no > > way to read the good data in a PMEM page with poison via DAX. So the > > flag would tell dax_direct_access() to again proceed in the face of > > errors, but then the driver's dax_copy_to_iter() operation could > > either read up to the precise byte offset of the error in the page, or > > autoreplace error data with zero's to try to maximize data recovery. > > Yes, it could. I like the idea - say RWF_IGNORE_HWERROR - to read > everything that can be read from the bad range because it's the > other half of the problem RWF_RESET_HWERROR is trying to address. > That is, the operation we want to perform on a range with an error > state is -data recovery-, not "reinitialisation". Data recovery > requires two steps: > > - "try to recover the data from the bad storage"; and > - "reinitialise the data and clear the error state" > > These naturally map to read() and write() operations, not > fallocate(). With RWF flags they become explicit data recovery > operations, unlike fallocate() which needs to imply that "writing > zeroes" == "reset hardware error state". While that reset method > may be true for a specific pmem hardware implementation it is not a > requirement for all storage hardware. It's most definitely not a > requirement for future storage hardware, either. > > It also means that applications have no choice in what data they can > use to reinitialise the damaged range with because fallocate() only > supports writing zeroes. If we've recovered data via a read() as you > suggest we could, then we can rebuild the data from other redundant > information and immediately write that back to the storage, hence > repairing the fault. > > That, in turn, allows the filesystem to turn the RWF_RESET_HWERROR > write into an exclusive operation and hence allow the > reinitialisation with the recovered/repaired state to run atomically > w.r.t. all other filesystem operations. i.e. the reset write > completes the recovery operation instead of requiring separate > "reset" and "write recovered data into zeroed range" steps that > cannot be executed atomically by userspace... /me nods Jane, want to take a run at patches for this ^^^?