• Brian Foster's avatar
    xfs: track preallocation separately in xfs_bmapi_reserve_delalloc() · 974ae922
    Brian Foster authored
    Speculative preallocation is currently processed entirely by the callers
    of xfs_bmapi_reserve_delalloc(). The caller determines how much
    preallocation to include, adjusts the extent length and passes down the
    resulting request.
    
    While this works fine for post-eof speculative preallocation, it is not
    as reliable for COW fork preallocation. COW fork preallocation is
    implemented via the cowextszhint, which aligns the start offset as well
    as the length of the extent. Further, it is difficult for the caller to
    accurately identify when preallocation occurs because the returned
    extent could have been merged with neighboring extents in the fork.
    
    To simplify this situation and facilitate further COW fork preallocation
    enhancements, update xfs_bmapi_reserve_delalloc() to take a separate
    preallocation parameter to incorporate into the allocation request. The
    preallocation blocks value is tacked onto the end of the request and
    adjusted to accommodate neighboring extents and extent size limits.
    Since xfs_bmapi_reserve_delalloc() now knows precisely how much
    preallocation was included in the allocation, it can also tag the inodes
    appropriately to support preallocation reclaim.
    
    Note that xfs_bmapi_reserve_delalloc() callers are not yet updated to
    use the preallocation mechanism. This patch should not change behavior
    outside of correctly tagging reflink inodes when start offset
    preallocation occurs (which the caller does not handle correctly).
    Signed-off-by: default avatarBrian Foster <bfoster@redhat.com>
    Reviewed-by: default avatarDave Chinner <dchinner@redhat.com>
    Signed-off-by: default avatarDave Chinner <david@fromorbit.com>
    
    974ae922
xfs_bmap.h 9.4 KB