lkml.org 
[lkml]   [2007]   [Feb]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: dirty balancing deadlock
    On Mon, 19 Feb 2007 18:11:55 +0100
    Miklos Szeredi <miklos@szeredi.hu> wrote:

    > How about this?

    I still don't understand this bug.

    > Solves the FUSE deadlock, but not the throttle_vm_writeout() one.
    > I'll try to tackle that one as well.
    >
    > If the per-bdi dirty counter goes below 16, balance_dirty_pages()
    > returns.
    >
    > Does the constant need to tunable? If it's too large, then the global
    > threshold is more easily exceeded. If it's too small, then in a tight
    > situation progress will be slower.
    >
    > Thanks,
    > Miklos
    >
    > Index: linux/mm/page-writeback.c
    > ===================================================================
    > --- linux.orig/mm/page-writeback.c 2007-02-19 17:32:41.000000000 +0100
    > +++ linux/mm/page-writeback.c 2007-02-19 18:05:28.000000000 +0100
    > @@ -198,6 +198,25 @@ static void balance_dirty_pages(struct a
    > dirty_thresh)
    > break;
    >
    > + /*
    > + * Acquit this producer if there's little or nothing
    > + * to write back to this particular queue
    > + *
    > + * Without this check a deadlock is possible in the
    > + * following case:
    > + *
    > + * - filesystem A writes data through filesystem B
    > + * - filesystem A has dirty pages over dirty_thresh
    > + * - writeback is started, this triggers a write in B
    > + * - balance_dirty_pages() is called synchronously
    > + * - the write to B blocks
    > + * - the writeback completes, but dirty is still over threshold
    > + * - the blocking write prevents futher writes from happening
    > + */
    > + if (atomic_long_read(&bdi->nr_dirty) +
    > + atomic_long_read(&bdi->nr_writeback) < 16)
    > + break;
    > +

    The problem seems to that little "- the write to B blocks".

    How come it blocks? I mean, if we cannot retire writes to that filesystem
    then we're screwed anyway.

    Anyway, I think I'll think about this issue a little later on. You might
    as well prepare full changelogs for your proposed changes, because we'll be
    needing them anyway.

    -
    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: 2007-02-21 22:39    [W:0.039 / U:30.712 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site