From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 48ED031AA9B for ; Wed, 4 Mar 2026 14:03:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772633035; cv=none; b=oh7pXBZNl7LOB+zq6ZX1IEMeN1I9St3Fc5JBxLVZp3v1R4hY7M4FxAkr+cRo28RtKLkVRxPuEOVNMgDSrxjjqJFIjsH4mWFZm0tMk8HWDlf+1So1qRJRmGn66WpzLU0b9yj+u1J6RGQGQT0KSD3Q7JjfelkXwcWa1sQnlM6TpJk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772633035; c=relaxed/simple; bh=1FzlaWuFLHg0MFaCBjxXLnOMEXdljE44wTExL0KRcvQ=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=Oxrjd5TG5oj0s6mBC+Lnvzvl+KTZvE8ultdXEly+meabViyHLamx5sp9+kYXctR5D0bjectpH9XEdbrw0O2HHhhz7YbG+epcp8uwM1UuoGvbL0StU1qjg4/TomYbu3/iUvZ54XYANP8Ttq4Hzth4RylKwdOp4DDLXE546BvJm14= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=NwhVFWa9; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="NwhVFWa9" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1772633032; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=+WIDnIhTkS9nHulT35K3M+7YjDAtdLL5oA2NtnO2on0=; b=NwhVFWa9W66aYd6Qnj7ZEFoh6DU9gNopawFiZ/cz2eG+CxdTLO8WW3d83xhDAA3qscYw5Y bm4ygz+VfF4ICGtuzs50ogCIsWmQ+uYBvVenu9Tj2jDvqwKgUT3/Ek/MopeG23dI7BzdVp tNE6lADNWtrbJQijqvQBLZEZZz+ecU8= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-614-cUu05l7LOtKvi_H8tPZRUA-1; Wed, 04 Mar 2026 09:03:47 -0500 X-MC-Unique: cUu05l7LOtKvi_H8tPZRUA-1 X-Mimecast-MFC-AGG-ID: cUu05l7LOtKvi_H8tPZRUA_1772633024 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 698F61955F02; Wed, 4 Mar 2026 14:03:39 +0000 (UTC) Received: from warthog.procyon.org.com (unknown [10.44.32.194]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id E9373180075F; Wed, 4 Mar 2026 14:03:32 +0000 (UTC) From: David Howells To: Matthew Wilcox , Christoph Hellwig , Jens Axboe , Leon Romanovsky Cc: David Howells , Christian Brauner , Paulo Alcantara , netfs@lists.linux.dev, linux-afs@lists.infradead.org, linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [RFC PATCH 00/17] netfs: [WIP] Keep track of folios in a segmented bio_vec[] chain Date: Wed, 4 Mar 2026 14:03:07 +0000 Message-ID: <20260304140328.112636-1-dhowells@redhat.com> Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Hi Willy, Christoph, et al., [!] This is a preview. Please don't expect this to fully compile or work. It's been somewhat tested with AFS and CIFS, but not 9P, Ceph or NFS - and will not build with Ceph or NFS at the moment. These patches get rid of folio_queue, rolling_buffer and ITER_FOLIOQ, replacing the folio queue construct used to manage buffers in netfslib with one based around a segmented chain of bio_vec arrays instead. There are three main aims here: (1) The kernel file I/O subsystem seems to be moving towards consolidating on the use of bio_vec arrays, so embrace this by moving netfslib to keep track of its buffers for buffered I/O in bio_vec[] form. (2) Netfslib already uses a bio_vec[] to handle unbuffered/DIO, so the number of different buffering schemes used can be reduced to just a single one. (3) Always send an entire filesystem RPC request message to a TCP socket with single kernel_sendmsg() call as this is faster, more efficient and doesn't require the use of corking as it puts the entire transmission loop inside of a single tcp_sendmsg(). For the replacement of folio_queue, a segmented chain of bio_vec arrays rather than a single monolithic array is provided: struct bvecq { struct bvecq *next; struct bvecq *prev; unsigned long long fpos; refcount_t ref; u32 priv; u16 nr_segs; u16 max_segs; bool inline_bv:1; bool free:1; bool unpin:1; bool discontig:1; struct bio_vec *bv; struct bio_vec __bv[]; }; The fields are: (1) next, prev - Link segments together in a list. I want this to be NULL-terminated linear rather than circular to make it possible to arbitrarily glue bits on the front. (2) fpos, discontig - Note the current file position of the first byte of the segment; all the bio_vecs in ->bv[] must be contiguous in the file space. The fpos can be used to find the folio by file position rather then from the info in the bio_vec. If there's a discontiguity, this should break over into a new bvecq segment with the discontig flag set (though this is redundant if you keep track of the file position). Note that the beginning and end file positions in a segment need not be aligned to any filesystem block size. (3) ref - Refcount. Each bvecq keeps a ref on the next. I'm not sure this is entirely necessary, but it makes sharing slices easier. (4) priv - Private data for the owner. Dispensible; currently only used for storing a debug ID for tracing in a patch not included here. (5) max_segs, nr_segs. The size of bv[] and the number of elements used. I've assumed a maximum of 65535 bio_vecs in the array (which would represent a ~1MiB allocation). (6) bv, __bv, inline_bv. bv points to the bio_vec[] array handled by this segment. This may begin at __bv and if it does inline_bv should be set (otherwise it's impossible to distinguish a separately allocated bio_vec[] that follows immediately by coincidence). (7) free, unpin. free is set if the memory pointed to by the bio_vecs needs freeing in some way upon I/O completion. unpin is set if this means using GUP unpinning rather than put_page(). I've also defined an iov_iter iterator type ITER_BVECQ to walk this sort of construct so that it can be passed directly to sendmsg() or block-based DIO (as cachefiles does). This series makes the following changes to netfslib: (1) The folio_queue chain used to hold folios for buffered I/O is replaced with a bvecq chain. Each bio_vec then holds (a portion of) one folio. Each bvecq holds a contiguous sequence of folios, but adjacent bvecqs in a chain may be discontiguous. (2) For unbuffered/DIO, the source iov_iter is extracted into a bvecq chain. (3) An abstract position representation ('bvecq_pos') is created that can used to hold a position in a bvecq chain. For the moment, this takes a ref on the bvecq it points to, but that may be excessive. (4) Buffer tracking is managed with three cursors: The load_cursor, at which new folios are added as we go; the dispatch_cursor, at which new subrequests' buffers start when they're created; and the collect_cursor, the point at which folios are being unlocked. Not all cursors are necessarily needed in all situations and during buffered writeback, we actually need a dispatch cursor per stream (one for the network filesystem and one for the cache). (5) ->prepare_read(), buffer setting up and ->issue_read() are merged, as are the write variants, with the filesystem calling back up to netfslib to prepare its buffer. This simplifies the process of setting up a subrequest. It may even make sense to have the filesystem allocate the subrequest. (6) For the moment, dispatch tracking is removed from netfs_io_request and netfs_io_stream. The problem is that we have several different ways (including in the retry code) in which we need to track things, some of which (e.g. retry) might happen simultaneously with the main dispatch, so keeping things separate helps. Netfslib sets up a context struct, passes it to ->issue_read/write(), which passes it back to netfs_prepare_read/write_buffer(). (7) Netfslib dispatches I/O by accumulating enough bufferage to dispatch at least one subrequest, then looping to generate as many as the filesystem wants to (they may be limited by other constraints, e.g. max RDMA segment count or negotiated max size). This loop could be moved down into the filesystem. A new method is provided by which netfslib can ask the filesystem to provide an estimate of the data that should be accumulated before dispatch begins. (8) Reading from the cache is now managed by querying the cache to provide a list of the next data extents within the cache. For the moment this uses FIEMAP, but should at some point into the future transition to using a block-fs metadata-independent way of tracking this. (9) AFS directories are switched to using a bvecq rather than a folio_queue to hold their contents. (10) Make CIFS use a bvecq rather than a folio_queue for holding a temporary encryption buffer. (11) CIFS RDMA is given the ability to extract ITER_BVECQ and support for extracting ITER_FOLIOQ, ITER_BVEC and ITER_KVEC is removed. (12) All the folio_queue and rolling_buffer code is removed. Two further things that I'm working on (but not in this branch) are: (1) Make it so that a filesystem can be given a copy of a subchain which it can then tack header and trailer protocol elements upon to form a single message (I have this working for cifs) and even join copies together with intervening protocol elements to form compounds. (2) Make it so that a filesystem can 'splice' out the contents of the TCP receive queue into a bvecq chain. This allows the socket lock to be dropped much more quickly and the copying of data read to the destination buffers to happen without the lock. I have this working for cifs too. Kernel recvmsg() doesn't then block kernel sendmsg() for anywhere near as long. There are also some things I want to consider for the future: (1) Create one or more batched iteration functions to 'unlock' all the folios in a bio_vec[], where 'unlock' is the appropriate action for ending a read or a write. Batching should hopefully also improve the efficiency of wrangling the marks on the xarray. Very often these marks are going to be represented by contiguous bits, so there may be a way to change them in bulk. (2) Rather than walking the bvecq chain to get each individual folio out via bv_page, use the file position stored on the bvecq and the sum of bv_len to iterate over the appropriate range in i_pages. (3) Change iov_iter to store the initial starting point and for iov_iter_revert() to reset to that and advance. This would (a) help prevent over-reversion and (b) dispense with the need for a prev pointer. (4) Use bvecq to replace scatterlist. One problem with replacing scatterlist is that crypto drivers like to glue bits on the front of the scatterlists they're given (something trivial with that API) - and this is one way to achieve it. The patches can also be found here: https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=netfs-next Thanks, David David Howells (17): netfs: Fix unbuffered/DIO writes to dispatch subrequests in strict sequence vfs: Implement a FIEMAP callback iov_iter: Add a segmented queue of bio_vec[] Add a function to kmap one page of a multipage bio_vec netfs: Add some tools for managing bvecq chains afs: Use a bvecq to hold dir content rather than folioq netfs: Add a function to extract from an iter into a bvecq cifs: Use a bvecq for buffering instead of a folioq cifs: Support ITER_BVECQ in smb_extract_iter_to_rdma() netfs: Switch to using bvecq rather than folio_queue and rolling_buffer cifs: Remove support for ITER_KVEC/BVEC/FOLIOQ from smb_extract_iter_to_rdma() netfs: Remove netfs_alloc/free_folioq_buffer() netfs: Remove netfs_extract_user_iter() iov_iter: Remove ITER_FOLIOQ netfs: Remove folio_queue and rolling_buffer netfs: Check for too much data being read netfs: Combine prepare and issue ops and grab the buffers on request Documentation/core-api/folio_queue.rst | 209 ------ Documentation/core-api/index.rst | 1 - fs/9p/vfs_addr.c | 34 +- fs/afs/dir.c | 41 +- fs/afs/dir_edit.c | 42 +- fs/afs/dir_search.c | 33 +- fs/afs/file.c | 27 +- fs/afs/fsclient.c | 8 +- fs/afs/inode.c | 18 +- fs/afs/internal.h | 16 +- fs/afs/write.c | 35 +- fs/afs/yfsclient.c | 6 +- fs/cachefiles/io.c | 350 +++++---- fs/ceph/addr.c | 109 +-- fs/ioctl.c | 29 +- fs/netfs/Makefile | 4 +- fs/netfs/buffered_read.c | 495 ++++++++----- fs/netfs/buffered_write.c | 2 +- fs/netfs/bvecq.c | 634 +++++++++++++++++ fs/netfs/direct_read.c | 123 ++-- fs/netfs/direct_write.c | 313 +++++++- fs/netfs/fscache_io.c | 6 - fs/netfs/internal.h | 164 ++++- fs/netfs/iterator.c | 313 +++----- fs/netfs/misc.c | 145 +--- fs/netfs/objects.c | 17 +- fs/netfs/read_collect.c | 124 ++-- fs/netfs/read_pgpriv2.c | 68 +- fs/netfs/read_retry.c | 226 +++--- fs/netfs/read_single.c | 177 +++-- fs/netfs/rolling_buffer.c | 222 ------ fs/netfs/stats.c | 6 +- fs/netfs/write_collect.c | 96 ++- fs/netfs/write_issue.c | 950 ++++++++++++++----------- fs/netfs/write_retry.c | 144 ++-- fs/nfs/fscache.c | 13 +- fs/smb/client/cifsglob.h | 2 +- fs/smb/client/cifssmb.c | 13 +- fs/smb/client/file.c | 149 ++-- fs/smb/client/smb2ops.c | 78 +- fs/smb/client/smb2pdu.c | 28 +- fs/smb/client/smbdirect.c | 152 +--- fs/smb/client/transport.c | 15 +- include/linux/bvec.h | 54 ++ include/linux/fiemap.h | 3 + include/linux/folio_queue.h | 282 -------- include/linux/fscache.h | 19 + include/linux/iov_iter.h | 66 +- include/linux/netfs.h | 177 +++-- include/linux/rolling_buffer.h | 61 -- include/linux/uio.h | 17 +- include/trace/events/netfs.h | 118 ++- lib/iov_iter.c | 395 +++++----- lib/scatterlist.c | 56 +- lib/tests/kunit_iov_iter.c | 183 ++--- net/9p/client.c | 8 +- 56 files changed, 3815 insertions(+), 3261 deletions(-) delete mode 100644 Documentation/core-api/folio_queue.rst create mode 100644 fs/netfs/bvecq.c delete mode 100644 fs/netfs/rolling_buffer.c delete mode 100644 include/linux/folio_queue.h delete mode 100644 include/linux/rolling_buffer.h