From patchwork Wed Dec 11 15:29:38 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jens Axboe X-Patchwork-Id: 11285345 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id B541E15AB for ; Wed, 11 Dec 2019 15:29:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8A73924679 for ; Wed, 11 Dec 2019 15:29:51 +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="rTSGHl4r" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387452AbfLKP3t (ORCPT ); Wed, 11 Dec 2019 10:29:49 -0500 Received: from mail-pl1-f194.google.com ([209.85.214.194]:42541 "EHLO mail-pl1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733306AbfLKP3s (ORCPT ); Wed, 11 Dec 2019 10:29:48 -0500 Received: by mail-pl1-f194.google.com with SMTP id x13so1546768plr.9 for ; Wed, 11 Dec 2019 07:29:48 -0800 (PST) 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=LqLfKfxDfr9ThyOm7S1FFMSYyKBD7N45F7A7qNmdNr0=; b=rTSGHl4r+r2nUquOl4X1P6mjxf6DJJue9R2uF6r06BuX5SNKubnOS2GOE0GcvYJEWV JPLfl77WzwgBSKgnRw5NQnJRZ4WKMfFCfksjoFx+sxGxEIJM/SLOsqXG7GDbqLKNPkE2 Rpq3U2T1f536DIOijDyiAEoq2P9aYyUzxEVUuDUubXkqimuNg5FWRpuFi+LREg+l6L93 5tu3Rrf3PM7hw58oztC6y7V9hNHCH+neTIGcy/VO3c8iJzC8eapKDKSKw/cmywg9CZ8E Z91T9XPei0hvJmqCd7qG++n92W004XeJCM9BdTQ+ijDuuQODyO7tNWRzJUv/49PN/nDB gYpg== 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=LqLfKfxDfr9ThyOm7S1FFMSYyKBD7N45F7A7qNmdNr0=; b=XIy1+3+6vK+PL/D9TEayV7m6wwk7EwbQFtYpJvFVWH30hz0AbXYUYD6/hCZjVhsPRf yms6vj3cOHnX4BJO2igbJh177IW5kkxnxZV+BK6h2w6XC6jOolveW9zoqgUL5ccnw2G2 SkM/l9odvM7T9nedTpi0zaVZy9MGrjD1i0sBtx+uKIRIcH4PT4dNN8IBDUn8IMfnHdAk lvz9BNHROCqCuBDyfa+F3SKLz/8Sbj1eKpDza53ioTZ8LuPlHLR/sftJCxrlRcCHNAtJ ZrKMX0MQw54yFFXPhX+GifENtfo89Ew7vTPc2gEZvvSmewaFVd0cmYYNEpIc+q9uNUCI Y3cg== X-Gm-Message-State: APjAAAVmwyxMYIpTOX45yhK989t3QFSCtbRf5n+EJlABEFRkb9x+lYAa /CjW6txB7wY5m2iYpRll4/0jAw== X-Google-Smtp-Source: APXvYqx1nknDUWAcCtnWR4lgVgOM29qBVuBTOdNVDNynssnsLxodyXf0nZ5cI9x5HuC2fXenMSA+ug== X-Received: by 2002:a17:902:848e:: with SMTP id c14mr4032994plo.36.1576078187819; Wed, 11 Dec 2019 07:29:47 -0800 (PST) Received: from x1.thefacebook.com ([2620:10d:c090:180::50da]) by smtp.gmail.com with ESMTPSA id n26sm3661882pgd.46.2019.12.11.07.29.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Dec 2019 07:29:46 -0800 (PST) From: Jens Axboe To: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org Cc: willy@infradead.org, clm@fb.com, torvalds@linux-foundation.org, david@fromorbit.com Subject: [PATCHSET v3 0/5] Support for RWF_UNCACHED Date: Wed, 11 Dec 2019 08:29:38 -0700 Message-Id: <20191211152943.2933-1-axboe@kernel.dk> X-Mailer: git-send-email 2.24.0 MIME-Version: 1.0 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Recently someone asked me how io_uring buffered IO compares to mmaped IO in terms of performance. So I ran some tests with buffered IO, and found the experience to be somewhat painful. The test case is pretty basic, random reads over a dataset that's 10x the size of RAM. Performance starts out fine, and then the page cache fills up and we hit a throughput cliff. CPU usage of the IO threads go up, and we have kswapd spending 100% of a core trying to keep up. Seeing that, I was reminded of the many complaints I here about buffered IO, and the fact that most of the folks complaining will ultimately bite the bullet and move to O_DIRECT to just get the kernel out of the way. But I don't think it needs to be like that. Switching to O_DIRECT isn't always easily doable. The buffers have different life times, size and alignment constraints, etc. On top of that, mixing buffered and O_DIRECT can be painful. Seems to me that we have an opportunity to provide something that sits somewhere in between buffered and O_DIRECT, and this is where RWF_UNCACHED enters the picture. If this flag is set on IO, we get the following behavior: - If the data is in cache, it remains in cache and the copy (in or out) is served to/from that. - If the data is NOT in cache, we add it while performing the IO. When the IO is done, we remove it again. With this, I can do 100% smooth buffered reads or writes without pushing the kernel to the state where kswapd is sweating bullets. In fact it doesn't even register. Comments appreciated! This should work on any standard file system, using either the generic helpers or iomap. I have tested ext4 and xfs for the right read/write behavior, but no further validation has been done yet. Patches are against current git, and can also be found here: https://git.kernel.dk/cgit/linux-block/log/?h=buffered-uncached fs/ceph/file.c | 2 +- fs/dax.c | 2 +- fs/ext4/file.c | 2 +- fs/iomap/apply.c | 26 ++++++++++- fs/iomap/buffered-io.c | 54 ++++++++++++++++------- fs/iomap/direct-io.c | 3 +- fs/iomap/fiemap.c | 5 ++- fs/iomap/seek.c | 6 ++- fs/iomap/swapfile.c | 2 +- fs/nfs/file.c | 2 +- include/linux/fs.h | 7 ++- include/linux/iomap.h | 10 ++++- include/uapi/linux/fs.h | 5 ++- mm/filemap.c | 95 ++++++++++++++++++++++++++++++++++++----- 14 files changed, 181 insertions(+), 40 deletions(-) Changes since v2: - Rework the write side according to Chinners suggestions. Much cleaner this way. It does mean that we invalidate the full write region if just ONE page (or more) had to be created, where before it was more granular. I don't think that's a concern, and on the plus side, we now no longer have to chunk invalidations into 15/16 pages at the time. - Cleanups Changes since v1: - Switch to pagevecs for write_drop_cached_pages() - Use page_offset() instead of manual shift - Ensure we hold a reference on the page between calling ->write_end() and checking the mapping on the locked page - Fix XFS multi-page streamed writes, we'd drop the UNCACHED flag after the first page