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Diffstat (limited to 'Documentation/filesystems/ext4/ondisk/bigalloc.rst')
| -rw-r--r-- | Documentation/filesystems/ext4/ondisk/bigalloc.rst | 22 |
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diff --git a/Documentation/filesystems/ext4/ondisk/bigalloc.rst b/Documentation/filesystems/ext4/ondisk/bigalloc.rst deleted file mode 100644 index c6d88557553c..000000000000 --- a/Documentation/filesystems/ext4/ondisk/bigalloc.rst +++ /dev/null @@ -1,22 +0,0 @@ -.. SPDX-License-Identifier: GPL-2.0 - -Bigalloc --------- - -At the moment, the default size of a block is 4KiB, which is a commonly -supported page size on most MMU-capable hardware. This is fortunate, as -ext4 code is not prepared to handle the case where the block size -exceeds the page size. However, for a filesystem of mostly huge files, -it is desirable to be able to allocate disk blocks in units of multiple -blocks to reduce both fragmentation and metadata overhead. The -`bigalloc <Bigalloc>`__ feature provides exactly this ability. The -administrator can set a block cluster size at mkfs time (which is stored -in the s\_log\_cluster\_size field in the superblock); from then on, the -block bitmaps track clusters, not individual blocks. This means that -block groups can be several gigabytes in size (instead of just 128MiB); -however, the minimum allocation unit becomes a cluster, not a block, -even for directories. TaoBao had a patchset to extend the “use units of -clusters instead of blocks” to the extent tree, though it is not clear -where those patches went-- they eventually morphed into “extent tree v2” -but that code has not landed as of May 2015. - |
