Re: [PATCH RFC] mm: Implement balance_dirty_pages() through waiting for flusher thread

[Peter Zijlstra <peterz@infradead.org>]

On Thu, 2010-06-17 at 20:04 +0200, Jan Kara wrote:
> +               if (bdi_stat(bdi, BDI_WRITTEN) >= bdi->wb_written_head)
> +                       bdi_wakeup_writers(bdi); 

For the paranoid amongst us you could make wb_written_head s64 and write
the above as:

  if (bdi_stat(bdi, BDI_WRITTEN) - bdi->wb_written_head > 0)

Which, if you assume both are monotonic and wb_written_head is always
within 2^63 of the actual bdi_stat() value, should give the same end
result and deal with wrap-around.

For when we manage to create a device that can write 2^64 pages in our
uptime :-)

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