On Mon, 19 Feb 2007 18:11:55 +0100 Miklos Szeredi <[EMAIL PROTECTED]> 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 [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
