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=-3.6 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 0B134C4727E for ; Mon, 28 Sep 2020 18:58:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BB71B207F7 for ; Mon, 28 Sep 2020 18:58:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="RYjU8DFG" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726589AbgI1S6k (ORCPT ); Mon, 28 Sep 2020 14:58:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53482 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726500AbgI1S6k (ORCPT ); Mon, 28 Sep 2020 14:58:40 -0400 Received: from mail-wm1-x344.google.com (mail-wm1-x344.google.com [IPv6:2a00:1450:4864:20::344]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 142AEC061755; Mon, 28 Sep 2020 11:58:40 -0700 (PDT) Received: by mail-wm1-x344.google.com with SMTP id d4so2169938wmd.5; Mon, 28 Sep 2020 11:58:40 -0700 (PDT) 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=qzLx+ktMPVhQAktjSFRBaXH0o66/8M0vKBETAdf1Yx4=; b=RYjU8DFGC3OKNRooUCoAsNT82Ecoc3NppLjTMfL3psheFuIc2gxNhNsy9kGyOSpsxe XkbyCfc6wdtuRVKVzZBlgdr5Hb3R4QiVZKlg8VUfDpYvSFQc9P8gIv0NDjkbH6BOSD6l /HpHbj0scL9/CIEc8UI0zMmlVHzd7TAtmoviJ1wlBQPJT/S0+bay2Sjpo4QYLhzYwh+3 nI4RyguxXOCD2pHc4MYHY+7p3p0wjm9FEod+wE2JE2gZcyDnZmT3y0B9q0TZ8aQ+P9sM K+xyknUeZDn1qoc/nrQVRgT2rvBGzdkzSGQs9aiti1mev+azxSxrx1RcbByRAKlaO0TM OnvA== 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=qzLx+ktMPVhQAktjSFRBaXH0o66/8M0vKBETAdf1Yx4=; b=gdhcab2bUgprb1aIjI60m0/1pqVKWCHCczDAQVuL9JKjfQDlFh/dohQ6HmlpttsaYo eScPit074XmBlSashv/0/ke1cP6diLSWo9lYAjnzx4c1gUhnDkgCEMS3jtvojBXwBP1/ cBAmcr1guz1GDSZdzgq4IGCGgI7HtMnChixIlIAI/ncBFpdnQRfaInIKTu/MjbENJ4lD JsDom4yUuqQL/9YJRqB3e5esKrAMYaE/uT1hm4PntoSvuvPnHEd283qIpzXNb5YwBgL4 BrYFUkSbCxgaGa9RbQt3btniiysAX+ljWA5khRISjPVdSum+QjzYuEtqen+c1ojbqiPI cawA== X-Gm-Message-State: AOAM532u/A0eACD/pvKhzo+Tvcr44lRskSaCJgtMenLBmyz8sTmioDt9 bAGDKWMidepzZtvy3NsacQYyhBbiDpmgutoaW6s= X-Google-Smtp-Source: ABdhPJxfvtSw/ZhL8NlA6HZcJ6dh91x4IhK4/Mxt/FgbMU2pzQdY4fBuBDZ7RHTYnZNdn803D/7Osnd3Adxo91wuQ/o= X-Received: by 2002:a7b:c1d9:: with SMTP id a25mr636586wmj.4.1601319518619; Mon, 28 Sep 2020 11:58:38 -0700 (PDT) MIME-Version: 1.0 References: <20200731091416.GA29634@infradead.org> <20200731094135.GA4104@infradead.org> <20200731125110.GA11500@infradead.org> <20200814081411.GA16943@infradead.org> <20200908151801.GA16742@infradead.org> In-Reply-To: From: Kanchan Joshi Date: Tue, 29 Sep 2020 00:28:12 +0530 Message-ID: Subject: Re: [PATCH v4 6/6] io_uring: add support for zone-append To: Damien Le Moal Cc: "hch@infradead.org" , Jens Axboe , Pavel Begunkov , Kanchan Joshi , "viro@zeniv.linux.org.uk" , "bcrl@kvack.org" , Matthew Wilcox , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-aio@kvack.org" , "io-uring@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-api@vger.kernel.org" , SelvaKumar S , Nitesh Shetty , Javier Gonzalez , Johannes Thumshirn , Naohiro Aota Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Fri, Sep 25, 2020 at 8:22 AM Damien Le Moal wrote: > > On 2020/09/25 2:20, Kanchan Joshi wrote: > > On Tue, Sep 8, 2020 at 8:48 PM hch@infradead.org wrote: > >> > >> On Mon, Sep 07, 2020 at 12:31:42PM +0530, Kanchan Joshi wrote: > >>> But there are use-cases which benefit from supporting zone-append on > >>> raw block-dev path. > >>> Certain user-space log-structured/cow FS/DB will use the device that > >>> way. Aerospike is one example. > >>> Pass-through is synchronous, and we lose the ability to use io-uring. > >> > >> So use zonefs, which is designed exactly for that use case. > > > > Not specific to zone-append, but in general it may not be good to lock > > new features/interfaces to ZoneFS alone, given that direct-block > > interface has its own merits. > > Mapping one file to a one zone is good for some use-cases, but > > limiting for others. > > Some user-space FS/DBs would be more efficient (less meta, indirection) > > with the freedom to decide file-to-zone mapping/placement. > > There is no metadata in zonefs. One file == one zone and the mapping between > zonefs files and zones is static, determined at mount time simply using report > zones. Zonefs files cannot be renamed nor deleted in anyway. Choosing a zonefs > file *is* the same as choosing a zone. Zonfes is *not* a POSIX file system doing > dynamic block allocation to files. The backing storage of files in zonefs is > static and fixed to the zone they represent. The difference between zonefs vs > raw zoned block device is the API that has to be used by the application, that > is, file descriptor representing the entire disk for raw disk vs file descriptor > representing one zone in zonefs. Note that the later has *a lot* of advantages > over the former: enables O_APPEND use, protects against bugs with user write > offsets mistakes, adds consistency of cached data against zone resets, and more. > > > - Rocksdb and those LSM style DBs would map SSTable to zone, but > > SSTable file may be two small (initially) and may become too large > > (after compaction) for a zone. > > You are contradicting yourself here. If a SSTable is mapped to a zone, then its > size cannot exceed the zone capacity, regardless of the interface used to access > the zones. And except for L0 tables which can be smaller (and are in memory > anyway), all levels tables have the same maximum size, which for zoned drives > must be the zone capacity. In any case, solving any problem in this area does > not depend in any way on zonefs vs raw disk interface. The implementation will > differ depending on the chosen interface, but what needs to be done to map > SSTables to zones is the same in both cases. > > > - The internal parallelism of a single zone is a design-choice, and > > depends on the drive. Writing multiple zones parallely (striped/raid > > way) can give better performance than writing on one. In that case one > > would want to file that seamlessly combines multiple-zones in a > > striped fashion. > > Then write a FS for that... Or have a library do it in user space. For the > library case, the implementation will differ for zonefs vs raw disk due to the > different API (regular file vs block devicer file), but the principles to follow > for stripping zones into a single storage object remain the same. ZoneFS is better when it is about dealing at single-zone granularity, and direct-block seems better when it is about grouping zones (in various ways including striping). The latter case (i.e. grouping zones) requires more involved mapping, and I agree that it can be left to application (for both ZoneFS and raw-block backends). But when an application tries that on ZoneFS, apart from mapping there would be additional cost of indirection/fd-management (due to file-on-files). And if new features (zone-append for now) are available only on ZoneFS, it forces application to use something that maynot be most optimal for its need. Coming to the original problem of plumbing append - I think divergence started because RWF_APPEND did not have any meaning for block device. Did I miss any other reason? How about write-anywhere semantics (RWF_RELAXED_WRITE or RWF_ANONYMOUS_WRITE flag) on block-dev. Zone-append works a lot like write-anywhere on block-dev (or on any other file that combines multiple-zones, in non-sequential fashion). > > Also it seems difficult (compared to block dev) to fit simple-copy TP > > in ZoneFS. The new > > command needs: one NVMe drive, list of source LBAs and one destination > > LBA. In ZoneFS, we would deal with N+1 file-descriptors (N source zone > > file, and one destination zone file) for that. While with block > > interface, we do not need more than one file-descriptor representing > > the entire device. With more zone-files, we face open/close overhead too. > > Are you expecting simple-copy to allow requests that are not zone aligned ? I do > not think that will ever happen. Otherwise, the gotcha cases for it would be far > too numerous. Simple-copy is essentially an optimized regular write command. > Similarly to that command, it will not allow copies over zone boundaries and > will need the destination LBA to be aligned to the destination zone WP. I have > not checked the TP though and given the NVMe NDA, I will stop the discussion here. TP is ratified, if that is the problem you are referring to. > filesend() could be used as the interface for simple-copy. Implementing that in > zonefs would not be that hard. What is your plan for simple-copy interface for > raw block device ? An ioctl ? filesend() too ? As as with any other user level > API, we should not be restricted to a particular device type if we can avoid it, > so in-kernel emulation of the feature is needed for devices that do not have > simple-copy or scsi extended copy. filesend() seems to me like the best choice > since all of that is already implemented there. At this moment, ioctl as sync and io-uring for async. sendfile() and copy_file_range() takes two fds....with that we can represent copy from one source zone to another zone. But it does not fit to represent larger copy (from N source zones to one destination zone). Not sure if I am clear, perhaps sending RFC would be better for discussion on simple-copy. > As for the open()/close() overhead for zonefs, may be some use cases may suffer > from it, but my tests with LevelDB+zonefs did not show any significant > difference. zonefs open()/close() operations are way faster than for a regular > file system since there is no metadata and all inodes always exist in-memory. > And zonefs() now supports MAR/MOR limits for O_WRONLY open(). That can simplify > things for the user. > > > -- > Damien Le Moal > Western Digital Research -- Joshi