On Fri, Dec 30, 2011 at 08:37:00AM +0530, Amit Sahrawat wrote: > On Fri, Dec 30, 2011 at 2:27 AM, Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > On Thu, Dec 29, 2011 at 01:10:49PM +0000, amit.sahrawat83@xxxxxxxxx wrote: > >> Hi, I am using a test setup which is doing write using multiple > >> threads using direct IO. The buffer size which is used to write is > >> 512KB. After continously running this for long duration - i > >> observe that number of extents in each file is getting > >> huge(2K..4K..). I observed that each extent is of 512KB(aligned to > >> write buffer size). I wish to have low number of extents(i.e, > >> reduce fragmentation)... In case of buffered IO- preallocation > >> works good alongwith the mount option 'allocsize'. Is there > >> anything which can be done for Direct IO? Please advice for > >> reducing fragmentation with direct IO. > > > > Direct IO does not do any implicit preallocation. The filesystem > > simply gets out of the way of direct IO as it is assumed you know > > what you are doing. > This is the supporting line I was looking for. > > > > i.e. you know how to use the fallocate() or ioctl(XFS_IOC_RESVSP64) > > calls to preallocate space or to set up extent size hints to use > > larger allocations than the IO being done during syscalls... > I tried to make use of preallocating space using > ioctl(XFS_IOC_RESVSP64) - but over time - this is also not working > well with the Direct I/O. Without knowing how you are using preallocation, I cannot comment on this. Can you describe how your application does IO (size, frequency, location in file, etc) and preallocation (same again), as well as xfs_bmap -vp <file> output of fragmented files? That way I have some idea of what your problem is and so might be able to suggest fixes... > Is there any call to set up extent size > also? please update I can try to make use of that also. `man xfsctl` and search for XFS_IOC_FSSETXATTR. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
