From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1036F40F8F9 for ; Thu, 30 Apr 2026 12:59:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777553964; cv=none; b=n/mrRknm44H+PJEWy1Ai606UeszxGG2y858mKgo9m0k+sQ72F3O3m4xrcEc0G8BDsf3Y6AieTBTPHKQBOonDdTdznUHU+glyum/djelWZwpXybp3YuQxINdsOnFcBChZFzENlbDNYiL2HqSq8aSy1y1XBl+hHMMx4rHvLgUPYVk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777553964; c=relaxed/simple; bh=RO9AMBx1mGt23i8/tpPEkax82KnBXZueuhiAZwqhCSQ=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=H2efkwd17v5ZIcJB6Uj7msAuFwu8xbFFTqV784Yq6XZuoNhiZE5r9w8WDpAeqBdMrwNuvvQzQ4tltAcysSgupfn4NCVaRsNA74YX36+iQjy0U6+5HqfzTo9T9h+Jp8QZekiw3Q8ynnb8EjMblBKEPlccSQug/qhEZlFyqSfj6/A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=R6zGpSHt; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="R6zGpSHt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E67B2C2BCB3; Thu, 30 Apr 2026 12:59:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777553963; bh=RO9AMBx1mGt23i8/tpPEkax82KnBXZueuhiAZwqhCSQ=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=R6zGpSHt1C0/DfwFv57/3EpAStBZVQB53ZQniPrzGIDOg6/W7vnZuF7go7DWKPqSV upMm8mvXGjsjHwBZa1/WnHmEi45LjcpsZ3a6X1Ju2ewux6oVuJ+NWzmmX4u4/yZCni R8LP9IQuVqklhLuRxcLaD9kf6Ce74qnpSCpKebVGYAo/Iy2lboNXwFHxunNEne3pON gfUa1eOgarBK3bNycrp6sjN45ltI+qRV1lJEWXXTMBxHuPhBdxthGlgEkCKTnFzyLR HY981xFC/pyQqQXb34dBwcCua6vpp/5EBBDEpFg50JfEklUjDPngZA8rv0q9FnoeHk DfGChNWMbmWRA== Message-ID: <8b120087b497c20aca3f0c73669d55c9fb779baa.camel@kernel.org> Subject: Re: [PATCH v2 00/14] fuse: add io-uring buffer rings and zero-copy From: Jeff Layton To: Joanne Koong , miklos@szeredi.hu Cc: bernd@bsbernd.com, axboe@kernel.dk, linux-fsdevel@vger.kernel.org Date: Thu, 30 Apr 2026 13:59:20 +0100 In-Reply-To: <20260402162840.2989717-1-joannelkoong@gmail.com> References: <20260402162840.2989717-1-joannelkoong@gmail.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 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ring and zero-copy capabilities to fuse over io-u= ring. >=20 > Using buffer rings has advantages over the non-buffer-ring (iovec) path: > - Reduced memory usage: in the iovec path, each entry has its own > dedicated payload buffer, requiring N buffers for N entries where each > buffer must be large enough to accommodate the maximum possible > payload size. With buffer rings, payload buffers are pooled and > selected on demand. Entries only hold a buffer while actively > processing a request with payload data. When incremental buffer > consumption is added, this will allow non-overlapping regions of a > single buffer to be used simultaneously across multiple requests, > further reducing memory requirements. > - Foundation for pinned buffers: the buffer ring headers and payloads > are now each passed in as a contiguous memory allocation, which allows > fuse to easily pin and vmap the entire region in one operation during > queue setup. This will eliminate the per-request overhead of having to > pin/unpin user pages and translate virtual addresses and is a > prerequisite for future optimizations like performing data copies > outside of the server's task context. >=20 > This series adds the capability to pin the underlying header and payload > buffers by setting init flags at registration time, depending on the user= 's > mlock limit. >=20 > Zero-copy (only for privileged servers) is also opt-in by setting an init= flag > at registration time. Zero-copy eliminates the memory copies between kern= el and > userspace for read/write/payload-heavy operations by allowing the server = to > directly operate on the client's underlying pages. >=20 > This series has a dependency on io-uring registered bvec buffers changes > in [1]. >=20 > The throughput improvements from pinned buffers and zero-copy depends on = how > much of the server's per-request latency is spent on data copying vs back= ing > I/O. When backing I/O dominates, the saved memcpy is a negligible fractio= n of > overall latency. Please also note that for the server to read/write > into the zero-copied pages, the read/write must go through io-uring > as an IORING_OP_READ_FIXED / IORING_OP_WRITE_FIXED operation. If the > server's backing I/O is instantaneous (eg served from cache), the > overhead of the additional io_uring operation may negate the savings > from eliminating the memcpy. >=20 > In benchmarks using passthrough_hp on a high-performance NVMe-backed > system, pinned headers and pinned payload buffers showed around a 10% > throughput improvement for direct randreads (~2150 MiB/s to ~2400 > MiB/s), a 4% improvement for direct sequential reads (~2510 MiB/s to > ~2620 MiB/s), a 8% improvement for buffered randreads (~2100 MiB/s to > ~2280 MiB/s), and a 6% improvement for buffered sequential reads (~2500 > MiB/s to ~2670 MiB/s). >=20 > Zero-copy showed around a 35% throughput improvement for direct > randreads (~2150 MiB/s to ~2900 MiB/s), a 15% improvement for direct > sequential reads (~2510 MiB/s to ~2900 MiB/s), a 15% improvement for > buffered randreads (~2100 MiB/s to ~2470 MiB/s), and a 10% improvement > for buffered sequential reads (~2500 MiB/s to ~2750 MiB/s). I didn't see > enough of a clear improvement for writes due to write latency being I/O > dominated. >=20 > The benchmarks were run using: > fio --name=3Dtest_run --ioengine=3Dsync --rw=3Drand{read,write} --bs=3D= 1M > --size=3D1G --numjobs=3D2 --ramp_time=3D30 --group_reporting=3D1 >=20 > To run the benchmark, please also add this patch [2]. >=20 > The libfuse changes can be found in [3]. To test the server, run: > sudo ~/libfuse/build/example/passthrough_hp ~/src ~/mounts/tmp > --nopassthrough -o io_uring_zero_copy -o io_uring_q_depth=3D8 > Once this series is merged, the libfuse changes will be tidied up and > submitted upstream. >=20 > Further optimizations for incremental buffer consumption, request > dispatching in current task context, and backing buffer integration with > IORING_OP_READ/IORING_OP_WRITE operations will be submitted as part of a > separate series. >=20 > Thanks, > Joanne=20 >=20 > [1] https://lore.kernel.org/io-uring/20260402160929.2749744-1-joannelkoon= g@gmail.com/T/#t > [2] https://lore.kernel.org/linux-fsdevel/20260326215127.3857682-2-joanne= lkoong@gmail.com/ > [3] https://github.com/joannekoong/libfuse/commits/zero_copy_v2/ >=20 > Changelog > --------- > v1: https://lore.kernel.org/linux-fsdevel/20260324224532.3733468-1-joanne= lkoong@gmail.com/ > v1 -> v2: > * Drop kernel managed buffers from io-uring infrastructure and instead mo= ve > logic into fuse. To later use buffers with io-uring requests natively w= ill > require fuse to place the backing buffer as a fixed buffer in a sparse = slot > for the server, but that will be added as an optimization in a separate > series. This makes the io-uring code cleaner and accomodates for more f= lexible > fuse user configurations (eg mlock limits) and easier setup (me) > * Run more benchmarks and get more numbers (me) > * Add visual diagrams and more documentatoin to commit messages and > documentation patch (Bernd) >=20 > Joanne Koong (14): > fuse: separate next request fetching from sending logic > fuse: refactor io-uring header copying to ring > fuse: refactor io-uring header copying from ring > fuse: use enum types for header copying > fuse: refactor setting up copy state for payload copying > fuse: support buffer copying for kernel addresses > fuse: use named constants for io-uring iovec indices > fuse: move fuse_uring_abort() from header to dev_uring.c > fuse: rearrange io-uring iovec and ent allocation logic > fuse: add io-uring buffer rings > fuse: add pinned headers capability for io-uring buffer rings > fuse: add pinned payload buffers capability for io-uring buffer rings > fuse: add zero-copy over io-uring > docs: fuse: add io-uring bufring and zero-copy documentation >=20 > .../filesystems/fuse/fuse-io-uring.rst | 189 +++ > fs/fuse/dev.c | 30 +- > fs/fuse/dev_uring.c | 1042 ++++++++++++++--- > fs/fuse/dev_uring_i.h | 86 +- > fs/fuse/fuse_dev_i.h | 8 +- > include/uapi/linux/fuse.h | 36 +- > 6 files changed, 1194 insertions(+), 197 deletions(-) >=20 >=20 > base-commit: 619fa72e875483dabf7683001496cc0ca4480aa6 Nice work, Joanne! This seems to be in great shape overall. I'll note that the first 9 patches or so (maybe modulo patch #6) could be merged in advance of the bigger io_uring changes. =20 --=20 Jeff Layton