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=-8.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 A06D3C433DF for ; Sat, 23 May 2020 01:50:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 593DA2072C for ; Sat, 23 May 2020 01:50:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="LAvGq9CG" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387475AbgEWBu6 (ORCPT ); Fri, 22 May 2020 21:50:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46912 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387453AbgEWBu6 (ORCPT ); Fri, 22 May 2020 21:50:58 -0400 Received: from mail-pl1-x643.google.com (mail-pl1-x643.google.com [IPv6:2607:f8b0:4864:20::643]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 83079C05BD43 for ; Fri, 22 May 2020 18:50:58 -0700 (PDT) Received: by mail-pl1-x643.google.com with SMTP id a13so5119263pls.8 for ; Fri, 22 May 2020 18:50:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=7l3Vl4XUCnVrv5zLlaIS2TAqW4v3YGdr3s+ckhxwo3k=; b=LAvGq9CG4T4SASualjrsfImwFHjrZ23/6PxdRJIQJ4CB67r5pCfVQlfHkmlkhrE17o vlrG0IeVUqgfrC0LHjA+Flocnfg3Z03dOs44FH3RPLcrPB9l8he10iFWcqjhkLfP3ZPI lkX6+1Gsd1Ny65q3n+Cu5/d2VSd36EV1pcSsbHCqYL0jCoKysJLQTtXwcVHTtO06HjF9 cr8h4KWHzcRkYb2Fc+NBSvWGcc4/gX6ZqX4d71d/Ybwur2aMHfV+aUt6J4jPxQ+IAS2p 9I2oqK48BHRVuQH/vFIjLYDuT+t0Ky0uAi5UG2mdfd0qP78H9zQUhHra4ZnPk4cE2L2w q+qg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=7l3Vl4XUCnVrv5zLlaIS2TAqW4v3YGdr3s+ckhxwo3k=; b=sv8VVNoCdYe/sc4ui4vFNbqc6qYPrGxrd8fhVT14Gg+RuwrYclEDfS8C60PeWz/GjG KPVdPUomkvCdQ43/f3qP5hEXsBMRtJ8EwnBh3pIEhNn2WuZnzh1RkzgweAVOOHwxTcJl DqmFoSqrCfW/Vn3/iPvLr1oFOULMroQOK7xnAUfk1Du3Y6ZeLLjfAWdXzczCztFpkgFP iKiTYyuwf5g4OLdapZiRn723ASgMbWOAZlJjRN8d+YN8P9VixMNek6mzP2zAkTC8fi4V 4qe14+hVfIbopR/KUedFyn8Qr8c/HuVBlvw6Ep32rqvmACBrQ9NX/g6bgaBqSXRmp9gg BkKw== X-Gm-Message-State: AOAM533i7fzyPNOsrsfC/4lfwMyIF3b8qViBOywA3KvlqArPELwLM9wh BE2gW3cFxtg6eeUp7ASVWke7wBYW5s8= X-Google-Smtp-Source: ABdhPJzbVANbqitIh8v7v51fEGKGFyBynVcF+TbM0Ms1gwAamMyyZ0DbB1Z9x3LfCBk3dayD3vcwSw== X-Received: by 2002:a17:90b:e0c:: with SMTP id ge12mr8085637pjb.3.1590198657579; Fri, 22 May 2020 18:50:57 -0700 (PDT) Received: from x1.lan ([2605:e000:100e:8c61:e0db:da55:b0a4:601]) by smtp.gmail.com with ESMTPSA id a71sm8255477pje.0.2020.05.22.18.50.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 22 May 2020 18:50:56 -0700 (PDT) From: Jens Axboe To: io-uring@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCHSET v2 RFC 0/11] Add support for async buffered reads Date: Fri, 22 May 2020 19:50:38 -0600 Message-Id: <20200523015049.14808-1-axboe@kernel.dk> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org We technically support this already through io_uring, but it's implemented with a thread backend to support cases where we would block. This isn't ideal. After a few prep patches, the core of this patchset is adding support for async callbacks on page unlock. With this primitive, we can simply retry the IO operation. With io_uring, this works a lot like poll based retry for files that support it. If a page is currently locked and needed, -EIOCBQUEUED is returned with a callback armed. The callers callback is responsible for restarting the operation. With this callback primitive, we can add support for generic_file_buffered_read(), which is what most file systems end up using for buffered reads. XFS/ext4/btrfs/bdev is wired up, but probably trivial to add more. The file flags support for this by setting FMODE_BUF_RASYNC, similar to what we do for FMODE_NOWAIT. Open to suggestions here if this is the preferred method or not. In terms of results, I wrote a small test app that randomly reads 4G of data in 4K chunks from a file hosted by ext4. The app uses a queue depth of 32. preadv for comparison: real 1m13.821s user 0m0.558s sys 0m11.125s CPU ~13% Mainline: real 0m12.054s user 0m0.111s sys 0m5.659s CPU ~32% + ~50% == ~82% This patchset: real 0m9.283s user 0m0.147s sys 0m4.619s CPU ~52% The CPU numbers are just a rough estimate. For the mainline io_uring run, this includes the app itself and all the threads doing IO on its behalf (32% for the app, ~1.6% per worker and 32 of them). Context switch rate is much smaller with the patchset, since we only have the one task performing IO. The goal here is efficiency. Async thread offload adds latency, and it also adds noticable overhead on items such as adding pages to the page cache. By allowing proper async buffered read support, we don't have X threads hammering on the same inode page cache, we have just the single app actually doing IO. Series can also be found here: https://git.kernel.dk/cgit/linux-block/log/?h=async-buffered.2 or pull from: git://git.kernel.dk/linux-block async-buffered.2 fs/block_dev.c | 2 +- fs/btrfs/file.c | 2 +- fs/ext4/file.c | 2 +- fs/io_uring.c | 102 ++++++++++++++++++++++++++++++++++++++ fs/xfs/xfs_file.c | 2 +- include/linux/blk_types.h | 3 +- include/linux/fs.h | 5 ++ include/linux/pagemap.h | 39 +++++++++++++++ mm/filemap.c | 83 +++++++++++++++++++++++++------ 9 files changed, 219 insertions(+), 21 deletions(-) Changes since v1: - Fix an issue with inline page locking - Fix a potential race with __wait_on_page_locked_async() - Fix a hang related to not setting page_match, thus missing a wakeup -- Jens Axboe