Re: [PATCH] Prevent large file writeback starvation

[David Chinner <dgc@sgi.com>]

On Sun, Feb 05, 2006 at 10:36:11PM -0800, Andrew Morton wrote:
> Andrew Morton <akpm@osdl.org> wrote:
> >
> > If so, why would that happen?  Take a look at wb_kupdate().  It's supposed
> >  to work *continuously* on the inodes until writeback_inodes() failed to
> >  write back enough pages.  It takes this as an indication that there's no
> >  more work to do at this time.
> > 
> >  It'd be interesting to take a look at what's happening in wb_kupdate().
> 
> Took a quick look at xfs_convert_page().  I don't immediately see a cause
> in there, but
> 
> 		if (count) {
> 			struct backing_dev_info *bdi;
> 
> 			bdi = inode->i_mapping->backing_dev_info;
> 			if (bdi_write_congested(bdi)) {
> 				wbc->encountered_congestion = 1;
> 				done = 1;
> 			} else if (--wbc->nr_to_write <= 0) {
> 				done = 1;
> 			}
> 		}
> 		xfs_start_page_writeback(page, wbc, !page_dirty, count);
> 
> shouldn't we be decrementing wbc->nr_to_write even if the queue is congested?

Yes, you are right. I'll fix it tomorrow.

Cheers,

Dave.
-- 
Dave Chinner
R&D Software Enginner
SGI Australian Software Group