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=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 BCEB0C433E1 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 9ADC220735 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 S2387486AbgEWBu6 (ORCPT ); Fri, 22 May 2020 21:50:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46910 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387427AbgEWBu6 (ORCPT ); Fri, 22 May 2020 21:50:58 -0400 Received: from mail-pj1-x1042.google.com (mail-pj1-x1042.google.com [IPv6:2607:f8b0:4864:20::1042]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 58AD3C061A0E for ; Fri, 22 May 2020 18:50:58 -0700 (PDT) Received: by mail-pj1-x1042.google.com with SMTP id ci21so5759034pjb.3 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=AJyrCe8RpmWqHgZOswFbMeJ4jVkZH5gejiePwT8wKBZDbRNjOrbC3F5GrWNgKMOwD3 JKvA3lgVaSOHwz1Aa2VGD8uNcQPWNdV93OXSsMV3l1kEraeRuaqyYD65wCtxrRQGlN0v pTd26SSfbrwfr0qF84Q2haDUlC+qDK6nhSVSApYSkqiG7BgU9zNU0gzQ+QrfTTwN9esm 1orSP+iepg656Pk7Pq1h++l+Amy0MsI6Kr+SnRaLoNQmUrZFggNfZ4JW5zTSOwEJQG50 rwxGdgz58p/NtXHisvKPNbf+GqivbdjNBUn+aOAjyQn7MFLhlZ6vfzsSQ73fI2j6a1zQ RQUw== X-Gm-Message-State: AOAM533FrLfEBJ/Hklz139OKuvLJGciOWbC+RX3/jyAD9PcR1kB5syb7 h4QMR+oUFD3DU72cLjkH56UgL14jYGs= 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: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@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