Re: [PATCH] Prevent large file writeback starvation

[Andrew Morton]

Andrew Morton <akpm@xxxxxxxx> 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?

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