• Coly Li's avatar
    gfs2: add flag REQ_PRIO for metadata I/O · e477b24b
    Coly Li authored
    When gfs2 does metadata I/O, only REQ_META is used as a metadata hint of
    the bio. But flag REQ_META is just a hint for block trace, not for block
    layer code to handle a bio as metadata request.
    
    For some of metadata I/Os of gfs2, A REQ_PRIO flag on the metadata bio
    would be very informative to block layer code. For example, if bcache is
    used as a I/O cache for gfs2, it will be possible for bcache code to get
    the hint and cache the pre-fetched metadata blocks on cache device. This
    behavior may be helpful to improve metadata I/O performance if the
    following requests hit the cache.
    
    Here are the locations in gfs2 code where a REQ_PRIO flag should be added,
    - All places where REQ_READAHEAD is used, gfs2 code uses this flag for
      metadata read ahead.
    - In gfs2_meta_rq() where the first metadata block is read in.
    - In gfs2_write_buf_to_page(), read in quota metadata blocks to have them
      up to date.
    These metadata blocks are probably to be accessed again in future, adding
    a REQ_PRIO flag may have bcache to keep such metadata in fast cache
    device. For system without a cache layer, REQ_PRIO can still provide hint
    to block layer to handle metadata requests more properly.
    Signed-off-by: default avatarColy Li <colyli@suse.de>
    Signed-off-by: default avatarBob Peterson <rpeterso@redhat.com>
    e477b24b
bmap.c 44.9 KB