lkml.org 
[lkml]   [2006]   [Apr]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: Lockless page cache test results


    On Thu, 27 Apr 2006, Nick Piggin wrote:
    > >
    > > Of course, with small files, the actual filename lookup is likely to be the
    > > real limiter.
    >
    > Although that's lockless so it scales. find_get_page will overtake it
    > at some point.

    filename lookup is only lockless for independent files. You end up getting
    the "dentry->d_lock" for a successful lookup in the lookup path, so if you
    have multiple threads looking up the same files (or - MUCH more commonly -
    directories), you're not going to be lockless.

    I don't know how we could improve it. I've several times thought that we
    _should_ be able to do the directory lookups under the rcu read lock and
    never touch their d_count or d_lock at all, but the locking against
    directory renaming depends very intimately on d_lock.

    It is _possible_ that we should be able to handle it purely with just
    memory ordering rather than depending on d_lock. That would be wonderful.

    Of course, we do actually scale pretty damn well already. I'm just saying
    that it's not perfect.

    See __d_lookup() for details.

    Linus
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2009-11-18 23:46    [W:0.023 / U:60.376 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site