-
由 Tao Ma 提交于
The ext4 multiblock allocator decides whether to use group or file preallocation based on the file size. When the file size reaches s_mb_stream_request (default is 16 blocks), it changes to use a file-specific preallocation. This is cool, but it has a tiny problem. See a simple script: mkfs.ext4 -b 1024 /dev/sda8 1000000 mount -t ext4 -o nodelalloc /dev/sda8 /mnt/ext4 for((i=0;i<5;i++)) do cat /mnt/4096>>/mnt/ext4/a #4096 is a file with 4096 characters. cat /mnt/4096>>/mnt/ext4/b done debuge4fs -R 'stat a' /dev/sda8|grep BLOCKS -A 1 And you get BLOCKS: (0-14):8705-8719, (15):2356, (16-19):8465-8468 So there are 3 extents, a bit strange for the lonely 15th logical block. As we write to the 16 blocks, we choose file preallocation in ext4_mb_group_or_file, but in ext4_mb_normalize_request, we meet with the 16*1024 range, so no preallocation will be carried. file b then reserves the space after '2356', so when when write 16, we start from another part. This patch just change the check in ext4_mb_group_or_file, so that for the lonely 15 we will still use group preallocation. After the patch, we will get: debuge4fs -R 'stat a' /dev/sda8|grep BLOCKS -A 1 BLOCKS: (0-15):8705-8720, (16-19):8465-8468 Looks more sane. Thanks. Signed-off-by: NTao Ma <tao.ma@oracle.com> Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>
cc483f10