• NeilBrown's avatar
    [PATCH] knfsd: stop NFSD writes from being broken into lots of little writes to filesystem · 29dbb3fc
    NeilBrown authored
    When NFSD receives a write request, the data is typically in a number of
    1448 byte segments and writev is used to collect them together.
    
    Unfortunately, generic_file_buffered_write passes these to the filesystem
    one at a time, so an e.g.  32K over-write becomes a series of partial-page
    writes to each page, causing the filesystem to have to pre-read those pages
    - wasted effort.
    
    generic_file_buffered_write handles one segment of the vector at a time as
    it has to pre-fault in each segment to avoid deadlocks.  When writing from
    kernel-space (and nfsd does) this is not an issue, so
    generic_file_buffered_write does not need to break and iovec from nfsd into
    little pieces.
    
    This patch avoids the splitting when  get_fs is KERNEL_DS as it is
    from NFSd.
    
    This issue was introduced by commit 6527c2bdAcked-by: default avatarNick Piggin <nickpiggin@yahoo.com.au>
    Cc: Norman Weathers <norman.r.weathers@conocophillips.com>
    Cc: Vladimir V. Saveliev <vs@namesys.com>
    Signed-off-by: default avatarNeil Brown <neilb@suse.de>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    29dbb3fc
filemap.c 62.6 KB