• Weston Andros Adamson's avatar
    nfs: add support for multiple nfs reqs per page · 2bfc6e56
    Weston Andros Adamson authored
    Add "page groups" - a circular list of nfs requests (struct nfs_page)
    that all reference the same page. This gives nfs read and write paths
    the ability to account for sub-page regions independently.  This
    somewhat follows the design of struct buffer_head's sub-page
    accounting.
    
    Only "head" requests are ever added/removed from the inode list in
    the buffered write path. "head" and "sub" requests are treated the
    same through the read path and the rest of the write/commit path.
    Requests are given an extra reference across the life of the list.
    
    Page groups are never rejoined after being split. If the read/write
    request fails and the client falls back to another path (ie revert
    to MDS in PNFS case), the already split requests are pushed through
    the recoalescing code again, which may split them further and then
    coalesce them into properly sized requests on the wire. Fragmentation
    shouldn't be a problem with the current design, because we flush all
    requests in page group when a non-contiguous request is added, so
    the only time resplitting should occur is on a resend of a read or
    write.
    
    This patch lays the groundwork for sub-page splitting, but does not
    actually do any splitting. For now all page groups have one request
    as pg_test functions don't yet split pages. There are several related
    patches that are needed support multiple requests per page group.
    Signed-off-by: default avatarWeston Andros Adamson <dros@primarydata.com>
    Signed-off-by: default avatarTrond Myklebust <trond.myklebust@primarydata.com>
    2bfc6e56
direct.c 28 KB