On Thu, May 21, 2020 at 07:53:09PM -0700, Darrick J. Wong wrote: > From: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > > When we're estimating a new speculative preallocation length for an > extending write, we should walk backwards through the extent list to > determine the number of number of blocks that are physically and > logically contiguous with the write offset, and use that as an input to > the preallocation size computation. > > This way, preallocation length is truly measured by the effectiveness of > the allocator in giving us contiguous allocations without being > influenced by the state of a given extent. This fixes both the problem > where ZERO_RANGE within an EOF can reduce preallocation, and prevents > the unnecessary shrinkage of preallocation when delalloc extents are > turned into unwritten extents. > > This was found as a regression in xfs/014 after changing delalloc writes > to create unwritten extents during writeback. > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> Looks good, Reviewed-by: Christoph Hellwig <hch@xxxxxx> A minor nitpick, though: > + struct xfs_iext_cursor ncur = *icur; /* struct copy */ > > + struct xfs_bmbt_irec prev, got; The comment is pretty pointless, as the struct copy is obviously form the syntax (and we do it for the xfs_iext_cursor structure in quite a few other places). Also please don't add empty lines between the variable declarations.
