On Tue, Dec 21, 2010 at 06:29:03PM +1100, Dave Chinner wrote: > From: Dave Chinner <dchinner@xxxxxxxxxx> > > A long standing problem for streaming write?? through the NFS server > has been that the NFS server opens and closes file descriptors on an > inode for every write. The result of this behaviour is that the > ->release() function is called on every close and that results in > XFS truncating speculative preallocation beyond the EOF. This has > an adverse effect on file layout when multiple files are being > written at the same time - they interleave their extents and can > result in severe fragmentation. > > To avoid this problem, keep a count of the number of ->release calls > made on an inode. For most cases, an inode is only going to be opened > once for writing and then closed again during it's lifetime in > cache. Hence if there are multiple ->release calls, there is a good > chance that the inode is being accessed by the NFS server. Hence > count up every time ->release is called while there are delalloc > blocks still outstanding on the inode. > > If this count is non-zero when ->release is next called, then do no > truncate away the speculative preallocation - leave it there so that > subsequent writes do not need to reallocate the delalloc space. This > will prevent interleaving of extents of different inodes written > concurrently to the same AG. > > If we get this wrong, it is not a big deal as we truncate > speculative allocation beyond EOF anyway in xfs_inactive() when the > inode is thrown out of the cache. Looks good. > The new counter in the struct xfs_inode fits into a hole in the > structure on 64 bit machines, so does not grow the size of the inode > at all. There's no counter any more. (the text further above could also use some minor updates for that) Reviewed-by: Christoph Hellwig <hch@xxxxxx> _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
