962e8a01ea
When moving extents, the current move_extent_per_page() process can only move extents of length PAGE_SIZE at a time, which is highly inefficient, especially when the fragmentation of the file is not particularly severe, this will result in a large number of unnecessary extent split and merge operations. Moreover, since the ext4 file system now supports large folios, using PAGE_SIZE as the processing unit is no longer practical. Therefore, introduce a new move extents method, mext_move_extent(). It moves one extent of the origin inode at a time, but not exceeding the size of a folio. The parameters for the move are passed through the new mext_data data structure, which includes the origin inode, donor inode, the mapping extent of the origin inode to be moved, and the starting offset of the donor inode. The move process is similar to move_extent_per_page() and can be categorized into three types: MEXT_SKIP_EXTENT, MEXT_MOVE_EXTENT, and MEXT_COPY_DATA. MEXT_SKIP_EXTENT indicates that the corresponding area of the donor file is a hole, meaning no actual space is allocated, so the move is skipped. MEXT_MOVE_EXTENT indicates that the corresponding areas of both the origin and donor files are unwritten, so no data needs to be copied; only the extents are swapped. MEXT_COPY_DATA indicates that the corresponding areas of both the origin and donor files contain data, so data must be copied. The data copying is performed in three steps: first, the data from the original location is read into the page cache; then, the extents are swapped, and the page cache is rebuilt to reflect the index of the physical blocks; finally, the dirty page cache is marked and written back to ensure that the data is written to disk before the metadata is persisted. One important point to note is that the folio lock and i_data_sem are held only during the moving process. Therefore, before moving an extent, it is necessary to check whether the sequence cookie of the area to be moved has changed while holding the folio lock. If a change is detected, it indicates that concurrent write-back operations may have occurred during this period, and the type of the extent to be moved can no longer be considered reliable. For example, it may have changed from unwritten to written. In such cases, return -ESTALE, and the calling function should reacquire the move extent of the original file and retry the movement. Signed-off-by: Zhang Yi <yi.zhang@huawei.com> Reviewed-by: Jan Kara <jack@suse.cz> Message-ID: <20251013015128.499308-10-yi.zhang@huaweicloud.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu> |
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README
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 reStructuredText 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.