• Steven Whitehouse's avatar
    [GFS2] Map multiple blocks at once where possible · 7a6bbacb
    Steven Whitehouse authored
    This is a tidy up of the GFS2 bmap code. The main change is that the
    bh is passed to gfs2_block_map allowing the flags to be set directly
    rather than having to repeat that code several times in ops_address.c.
    
    At the same time, the extent mapping code from gfs2_extent_map has
    been moved into gfs2_block_map. This allows all calls to gfs2_block_map
    to map extents in the case that no allocation is taking place. As a
    result reads and non-allocating writes should be faster. A quick test
    with postmark appears to support this.
    
    There is a limit on the number of blocks mapped in a single bmap
    call in that it will only ever map blocks which are pointed to
    from a single pointer block. So in other words, it will never try
    to do additional i/o in order to satisfy read-ahead. The maximum
    number of blocks is thus somewhat less than 512 (the GFS2 4k block
    size minus the header divided by sizeof(u64)). I've further limited
    the mapping of "normal" blocks to 32 blocks (to avoid extra work)
    since readpages() will currently read a maximum of 32 blocks ahead (128k).
    
    Some further work will probably be needed to set a suitable value
    for DIO as well, but for now thats left at the maximum 512 (see
    ops_address.c:gfs2_get_block_direct).
    
    There is probably a lot more that can be done to improve bmap for GFS2,
    but this is a good first step.
    Signed-off-by: default avatarSteven Whitehouse <swhiteho@redhat.com>
    7a6bbacb
bmap.h 1.11 KB