Are you using FALLOC_FL_KEEP_SIZE? If so, commit a379cd1d6bb00f9f5d2759d4a5621a884df5914e fixed a bug with this (but I don't know offhand which kernel this went into). Curt On Fri, Oct 29, 2010 at 11:26 AM, George Kola <georgekola@xxxxxxxxx> wrote: > 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 > -- 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
