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authorTheodore Ts'o <tytso@mit.edu>2010-01-01 02:41:30 -0500
committerTheodore Ts'o <tytso@mit.edu>2010-01-01 02:41:30 -0500
commit9d0be50230b333005635967f7ecd4897dbfd181b (patch)
tree59aefe29e33284e1d904b23eaf2cc98994431374 /Documentation/blackfin
parentee5f4d9cdf32fd99172d11665c592a288c2b1ff4 (diff)
ext4: Calculate metadata requirements more accurately
In the past, ext4_calc_metadata_amount(), and its sub-functions ext4_ext_calc_metadata_amount() and ext4_indirect_calc_metadata_amount() badly over-estimated the number of metadata blocks that might be required for delayed allocation blocks. This didn't matter as much when functions which managed the reserved metadata blocks were more aggressive about dropping reserved metadata blocks as delayed allocation blocks were written, but unfortunately they were too aggressive. This was fixed in commit 0637c6f, but as a result the over-estimation by ext4_calc_metadata_amount() would lead to reserving 2-3 times the number of pending delayed allocation blocks as potentially required metadata blocks. So if there are 1 megabytes of blocks which have been not yet been allocation, up to 3 megabytes of space would get reserved out of the user's quota and from the file system free space pool until all of the inode's data blocks have been allocated. This commit addresses this problem by much more accurately estimating the number of metadata blocks that will be required. It will still somewhat over-estimate the number of blocks needed, since it must make a worst case estimate not knowing which physical blocks will be needed, but it is much more accurate than before. Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
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