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8394a97c4b
Online repair of the reverse-mapping btrees presens some unique challenges. To construct a new reverse mapping btree, we must scan the entire filesystem, but we cannot afford to quiesce the entire filesystem for the potentially lengthy scan. For rmap btrees, therefore, we relax our requirements of totally atomic repairs. Instead, repairs will scan all inodes, construct a new reverse mapping dataset, format a new btree, and commit it before anyone trips over the corruption. This is exactly the same strategy as was used in the quotacheck and nlink scanners. Unfortunately, the xfarray cannot perform key-based lookups and is therefore unsuitable for supporting live updates. Luckily, we already a data structure that maintains an indexed rmap recordset -- the existing rmap btree code! Hence we port the existing btree and buffer target code to be able to create a btree using the xfile we developed earlier. Live hooks keep the in-memory btree up to date for any resources that have already been scanned. This approach is not maximally memory efficient, but we can use the same rmap code that we do everywhere else, which provides improved stability without growing the code base even more. Note that in-memory btree blocks are always page sized. This patchset modifies the kernel xfs buffer cache to be capable of using a xfile (aka a shmem file) as a backing device. It then augments the btree code to support creating btree cursors with buffers that come from a buftarg other than the data device (namely an xfile-backed buftarg). For the userspace xfs buffer cache, we instead use a memfd or an O_TMPFILE file as a backing device. This has been running on the djcloud for months with no problems. Enjoy! Signed-off-by: Darrick J. Wong <djwong@kernel.org> -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQQ2qTKExjcn+O1o2YRKO3ySh0YRpgUCZdlBYgAKCRBKO3ySh0YR pqHwAQCjqXCvbqrWgMC/oYWuuDkYul79mqZw7PF58tdWpsOnzwD/dkyt7FBpAaAA GCaCIpWwOPErZ0LMT2fH6CqZyndSxw8= =vdwY -----END PGP SIGNATURE----- Merge tag 'in-memory-btrees-6.9_2024-02-23' of https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux into xfs-6.9-mergeC xfs: support in-memory btrees Online repair of the reverse-mapping btrees presens some unique challenges. To construct a new reverse mapping btree, we must scan the entire filesystem, but we cannot afford to quiesce the entire filesystem for the potentially lengthy scan. For rmap btrees, therefore, we relax our requirements of totally atomic repairs. Instead, repairs will scan all inodes, construct a new reverse mapping dataset, format a new btree, and commit it before anyone trips over the corruption. This is exactly the same strategy as was used in the quotacheck and nlink scanners. Unfortunately, the xfarray cannot perform key-based lookups and is therefore unsuitable for supporting live updates. Luckily, we already a data structure that maintains an indexed rmap recordset -- the existing rmap btree code! Hence we port the existing btree and buffer target code to be able to create a btree using the xfile we developed earlier. Live hooks keep the in-memory btree up to date for any resources that have already been scanned. This approach is not maximally memory efficient, but we can use the same rmap code that we do everywhere else, which provides improved stability without growing the code base even more. Note that in-memory btree blocks are always page sized. This patchset modifies the kernel xfs buffer cache to be capable of using a xfile (aka a shmem file) as a backing device. It then augments the btree code to support creating btree cursors with buffers that come from a buftarg other than the data device (namely an xfile-backed buftarg). For the userspace xfs buffer cache, we instead use a memfd or an O_TMPFILE file as a backing device. Signed-off-by: Darrick J. Wong <djwong@kernel.org> Signed-off-by: Chandan Babu R <chandanbabu@kernel.org> * tag 'in-memory-btrees-6.9_2024-02-23' of https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux: xfs: launder in-memory btree buffers before transaction commit xfs: support in-memory btrees xfs: add a xfs_btree_ptrs_equal helper xfs: support in-memory buffer cache targets xfs: teach buftargs to maintain their own buffer hashtable |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.