| Message ID | 1267171522-17439-1-git-send-email-tao.ma@oracle.com |
|---|---|
| State | Accepted, archived |
| Headers | show |
Thanks, this patch makes sense. I've added it to the ext4 patch queue. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index d34afad..301b173 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -3938,7 +3938,7 @@ static void ext4_mb_group_or_file(struct ext4_allocation_context *ac) /* don't use group allocation for large files */ size = max(size, isize); - if (size >= sbi->s_mb_stream_request) { + if (size > sbi->s_mb_stream_request) { ac->ac_flags |= EXT4_MB_STREAM_ALLOC; return; }
ext4 predicts whether we use group or file preallocation by the file size. So in general, if the file size has reached s_mb_stream_request(default is 16 blocks), it will change to use file 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 15. The reason is that if blocksize is 1K, 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: Tao Ma <tao.ma@oracle.com> Cc: "Theodore Ts'o" <tytso@mit.edu> --- fs/ext4/mballoc.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)