I am using RHEL (CentOS) 5.5 with kernel 2.6.18-194.17.4.el5 and ext4. I posted to RHEL bugzilla and they requested me to post it here. I wrote a program that fallocates space for a file. It does not know the file size apriori and uses a heuristic. If the final file size is less than the allocated space, I free up the extra space with truncate. I found that freeing up did not work so I ended up doing two truncates -- truncate(size+1) followed by truncate(size) as suggested in http://kerneltrap.org/mailarchive/linux-ext4/2009/7/21/6243463. I now find that the freed space is not given back till a unmount+ mount. I detected this by finding disks full even though the used space was lesser. I did the standard tests 1. Stopped all program having handles open to files on that partition 2. Verified with lsof that there are no open handles to files in that partition Still there was a mismatch. e.g. see below e.g. bash-3.2# mount | grep hadoop_data /dev/mapper/vg0-data on /hadoop_data type ext4 (rw,noatime,barrier=0,journal_checksum) bash-3.2# mount | grep hadoop_data /dev/mapper/vg0-data on /hadoop_data type ext4 (rw,noatime,barrier=0,journal_checksum) bash-3.2# du -h /hadoop_data/ | tail -1 328G /hadoop_data/ bash-3.2# df -h /hadoop_data/ Filesystem Size Used Avail Use% Mounted on /dev/mapper/vg0-data 745G 592G 117G 84% /hadoop_data After unmount + mount, I find this bash-3.2# umount /hadoop_data/ bash-3.2# mount /hadoop_data/ bash-3.2# df -h /hadoop_data/ Filesystem Size Used Avail Use% Mounted on /dev/mapper/vg0-data 745G 328G 380G 47% /hadoop_data Version-Release number of selected component (if applicable): RHEL (CentOS) 5.5 with kernel 2.6.18-194.17.4.el5 and ext4. How reproducible: All the time. Steps to Reproduce: Have a program 1. Open a file on ext4 partition 2. Fallocate space for that file say 20 GB 3. Write data to the file (but less than the allocated space) say 10 GB 4. Close the file 5. Call truncate(file-path, size+1), truncate(file-path,size) on that file to give up the space (observed that the space is given up using filefrag) 6. Use du and df on that ext4 partition to find that the mismatch -George -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
