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 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 661A8C04A6B for ; Wed, 8 May 2019 18:12:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3C9C120644 for ; Wed, 8 May 2019 18:12:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="p0zgYRav" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726771AbfEHSMV (ORCPT ); Wed, 8 May 2019 14:12:21 -0400 Received: from mail-qt1-f173.google.com ([209.85.160.173]:34340 "EHLO mail-qt1-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726558AbfEHSMV (ORCPT ); Wed, 8 May 2019 14:12:21 -0400 Received: by mail-qt1-f173.google.com with SMTP id j6so24342747qtq.1; Wed, 08 May 2019 11:12:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:subject:to:cc:references:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=3EtBSWKXvWhK5ahRNqbD9aitgAQyO29KGemVXp7iPbI=; b=p0zgYRavLfnFw6tzfy5RxlKX+Yaq4nP5orA7fNJUfhm/WwQk9NPg0U19DrwONAJZiD 5zjay4uKP5n4jLY/lvGu4OaU8DB5+H39KVI8kq2rdgEVdXqbLHkkmJO47BnFCcIfQB4g vFtfHGktCXBuZ6KyCOuOQE8EASJnmCIvVsmsFNzte4Dm3e0Q6XqBeBCi/OmkwPXxzq0v X3C0FlDW+rxGTqg1fuWwY0Ncaf4ZGYpEcFZUT/WE9YLXSDaJdC8Dg8VBOah9yEnmvE+Q t/IIgk+HQRstPF/Wizgm7lpY0JNvzavtyF2FGNCgEgVU6NzC7d67GLUTbdyXu67LbZZv Y7xg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:subject:to:cc:references:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=3EtBSWKXvWhK5ahRNqbD9aitgAQyO29KGemVXp7iPbI=; b=Otr/t0H5J4fDi3J0g4H70qDDipbhwDzBfSHLzJ2iQ9l+hI+ZDb0opfqJ/xpvpOljdN gyTvufFxA5SAAKmq7VCN0xmCJySdVJxTLGv6ih8r44U08XUxo6CAGB/KG/iUweNEFf8Y yEExZeyV24YmzPBW1w2zrTQlY5uOCRrMgx2abJa5TsfcBLchDY6HYpTlzLacBvNy6hi6 sWOw2LuhF2icr5exy4Tfk6X4XpOD6YovIu53bYl3sx+++JAx4OffB1RJMsjLU+MbmV8I 07uvyAWiYn8uGPocFew5YRr8rCgjkBkG0yAIRrbBYAEeLCMan98iyJWLF/VQLcxuVNSR sQvQ== X-Gm-Message-State: APjAAAWI0lfu8S95j//gZBbuWjZKacADDdlM/wg0qU4713Rq4ktEmRoO 7yA3tHPxDkJcLpI/HYohy9nby9OgdI8= X-Google-Smtp-Source: APXvYqyoob7gPuJlyn5s8stW5f2v6LO1MyR170RnlDAEDFVoylkYDdtKbUfyxATBcAnb7o/wAAm4qw== X-Received: by 2002:ad4:51c2:: with SMTP id p2mr15308535qvq.64.1557339140076; Wed, 08 May 2019 11:12:20 -0700 (PDT) Received: from localhost.localdomain ([163.114.130.128]) by smtp.gmail.com with ESMTPSA id r47sm8814874qte.70.2019.05.08.11.12.18 (version=TLS1_3 cipher=AEAD-AES128-GCM-SHA256 bits=128/128); Wed, 08 May 2019 11:12:19 -0700 (PDT) From: Ric Wheeler Subject: Re: Testing devices for discard support properly To: "Martin K. Petersen" Cc: Dave Chinner , Jens Axboe , linux-block@vger.kernel.org, Linux FS Devel , lczerner@redhat.com References: <4a484c50-ef29-2db9-d581-557c2ea8f494@gmail.com> <20190507220449.GP1454@dread.disaster.area> <20190508011407.GQ1454@dread.disaster.area> <13b63de0-18bc-eb24-63b4-3c69c6a007b3@gmail.com> <0a16285c-545a-e94a-c733-bcc3d4556557@gmail.com> Message-ID: <99144ff8-4f2c-487d-a366-6294f87beb58@gmail.com> Date: Wed, 8 May 2019 14:12:18 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org (stripped out the html junk, resending) On 5/8/19 1:25 PM, Martin K. Petersen wrote: >>> WRITE SAME also has an ANCHOR flag which provides a use case we >>> currently don't have fallocate plumbing for: Allocating blocks without >>> caring about their contents. I.e. the blocks described by the I/O are >>> locked down to prevent ENOSPC for future writes. >> Thanks for that detail! Sounds like ANCHOR in this case exposes >> whatever data is there (similar I suppose to normal block device >> behavior without discard for unused space)? Seems like it would be >> useful for virtually provisioned devices (enterprise arrays or >> something like dm-thin targets) more than normal SSD's? > It is typically used to pin down important areas to ensure one doesn't > get ENOSPC when writing journal or metadata. However, these are > typically the areas that we deliberately zero to ensure predictable > results. So I think the only case where anchoring makes much sense is on > devices that do zero detection and thus wouldn't actually provision N > blocks full of zeroes. This behavior at the block layer might also be interesting for something like the VDO device (compression/dedup make it near impossible to predict how much space is really there since it is content specific). Might be useful as a way to hint to VDO about how to give users a promise of "at least this much" space? If the content is good for compression or dedup, you would get more, but never see less. Ric