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 850E1C433E0 for ; Fri, 22 May 2020 20:24:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 67E0820759 for ; Fri, 22 May 2020 20:24:16 +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="eqDNPpx4" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731021AbgEVUYP (ORCPT ); Fri, 22 May 2020 16:24:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52540 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731018AbgEVUXU (ORCPT ); Fri, 22 May 2020 16:23:20 -0400 Received: from mail-pf1-x441.google.com (mail-pf1-x441.google.com [IPv6:2607:f8b0:4864:20::441]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B86BAC08C5C0 for ; Fri, 22 May 2020 13:23:18 -0700 (PDT) Received: by mail-pf1-x441.google.com with SMTP id y18so5666546pfl.9 for ; Fri, 22 May 2020 13:23:18 -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=ab5UacrWfMxKEXoTvw+r9z4XQbT+Q8YnFiaJgTUI+4I=; b=eqDNPpx4Yx8kNVwfnScgWQcHCBoZ7c5VUXgFz6LhgOr5p2F74g+oGbfecIsGYaSdQs cN0iE1NTgsEPLNpzJivRdEWhg9BW19nqRF8lhW9X5Fq7xSEuRwCK62gHH2vV1cnEQw8B W81tcC2QqdCxFrXjlmBBiYa6tgTT0IPQmvfa70K5s6O0NQLRGU5zVc9XZuoU5sU7I1QY IUkS4AjhttnQaz0cBpR1uhjgCorl4QNOUjv5pKZdqcReX/1aWYc7/JAaMp8Skg6SVml4 hTZecBKBZqHFzZGr1DxRlwnPkzB9Ptgt/1WHt4IqANo3U5t7g1faSXe8aQH9d8vwp66g qR5w== 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=ab5UacrWfMxKEXoTvw+r9z4XQbT+Q8YnFiaJgTUI+4I=; b=uEgaqwEymIjQvRuuzhhWYkc331hDI6q+NNVNXYGmW/2LYQeV+QNjbu8EAT28CBdh8e oiNkM1OkTB1iJ8kJCmECh/4O3Y8hBEpVz/uJojoaAigYuVUj4PCttTYGJBUq8pZ5NVqC wmz1q0FDVLqWuDzFVuzIGHHFNUlXmEc47hGXFt7kfCWDWWdzNr7AOoJlq3U40pImkOnD 6tjr+1uDrkDQEnYTUdwnDDDyPlt2TQp9dpmesX/PNYC3UcW4qCSYlZ1lU7uwAvBlK+DX DltJp9zXbZGyCxeeBJBX0jEMNnDZqY0QrTmk9SNADKkg/5OPZo2uD8O2tJAuqxRF3QMz OfHg== X-Gm-Message-State: AOAM530D/r7dUs3YyoK7hsP2/Bf6utTsu0O7M5BUzMIZL0OIBxZSZtJi Xc/viU0dmvA1l+ORSjeWFXGBomaDYKk= X-Google-Smtp-Source: ABdhPJxtEjcPbn/EzO8+oMsGHO+DVMqdzYGBQ9GPRAGdMGqIhRdRmBv87H0lkbc7rIesvLYkkBKQ6g== X-Received: by 2002:a63:2f41:: with SMTP id v62mr15278765pgv.178.1590178997595; Fri, 22 May 2020 13:23:17 -0700 (PDT) Received: from x1.lan ([2605:e000:100e:8c61:e0db:da55:b0a4:601]) by smtp.gmail.com with ESMTPSA id e19sm7295561pfn.17.2020.05.22.13.23.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 22 May 2020 13:23:17 -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 RFC 0/11] Add support for async buffered reads Date: Fri, 22 May 2020 14:23:00 -0600 Message-Id: <20200522202311.10959-1-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 or pull from: git://git.kernel.dk/linux-block async-buffered fs/block_dev.c | 2 +- fs/btrfs/file.c | 2 +- fs/ext4/file.c | 2 +- fs/io_uring.c | 101 ++++++++++++++++++++++++++++++++++++++ fs/xfs/xfs_file.c | 2 +- include/linux/blk_types.h | 3 +- include/linux/fs.h | 5 ++ include/linux/pagemap.h | 40 +++++++++++++++ mm/filemap.c | 71 +++++++++++++++++++++------ 9 files changed, 207 insertions(+), 21 deletions(-) -- Jens Axboe