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. Is there any call to set up extent size also? please update I can try to make use of that also. Thanks & Regards, Amit Sahrawat > > Cheers, > > Dave. > -- > Dave Chinner > david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
