On Tue, May 08, 2012 at 11:24:52AM +0800, Zhu Han wrote: > On Tue, May 8, 2012 at 7:59 AM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > > On Mon, May 07, 2012 at 08:44:17PM +0800, Zhu Han wrote: > > > Seems like xfs of CentOS 6.X occupies much more storage space than > > desired > > > if fallocate is used against the file. Here is the step to reproduce it: > > > > You test case is not doing what you think it is doing. > > Thanks for pointing it out. > > > > By the way, is it normal when the file is moved around after the > > > preallocated region is filled with data? > > > > > > $ uname -r > > > 2.6.32-220.7.1.el6.x86_64 > > > > > > $fallocate -n --offset 0 -l 1G file ---->Write a little more data than > > > the preallocated size > > > > > > $ xfs_bmap -p -vv file > > > file: > > > EXT: FILE-OFFSET BLOCK-RANGE AG AG-OFFSET > > > TOTAL FLAGS > > > 0: [0..2097151]: 2593408088..2595505239 21 (29420144..31517295) > > > 2097152 10000 > > > > > > $ dd if=/dev/zero of=/tmp/file bs=1M count=1026 conv=fsync > > > > That does a truncate first, removing all the preallocated space. Use > > conv=notrunc to avoid this. Hence the space allocated by this > > new write is different to the space allocated by the above > > preallocation. The file has not been moved, the filesystem just did > > what you asked it to do. > > > > > > > > $ xfs_bmap -p -vv file > > > file: > > > EXT: FILE-OFFSET BLOCK-RANGE AG AG-OFFSET > > > TOTAL FLAGS > > > 0: [0..4194303]: 2709184016..2713378319 22 (23101408..27295711) > > > 4194304 00000 > > > > And so now you've triggered the speculative delayed allocation > > beyond EOF, which is normal behaviour. Hence there are currently > > unused blocks beyond EOF which will get removed either when the next > > close(fd) occurs on the file or the inode is removed from the cache. > > > > Close(fd) should be invoked before dd quits. But why the extra blocks > beyond EOF are not freed? The removal is conditional on how many times the fd has been closed with dirty data on the inode. > The only way I found to remove the extra blocks is truncate the file to its > real size. If the close() didn't remove them, they will be removed when the inode ages out of the cache. Why do you even care about them? Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
