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SubjectRe: [PATCH 03/13] writeback: per-task rate limit on balance_dirty_pages()
On Wed, Nov 24, 2010 at 06:23:07PM +0800, Peter Zijlstra wrote:
> On Wed, 2010-11-17 at 12:27 +0800, Wu Fengguang wrote:
> > + if (unlikely(current->nr_dirtied >= current->nr_dirtied_pause ||
> > + bdi->dirty_exceeded)) {
> > + balance_dirty_pages(mapping, current->nr_dirtied);
> > + current->nr_dirtied = 0;
> > }
>
> Was it a conscious choice to use
> current->nr_dirtied = 0
> over
> current->nr_dirtied -= current->nr_dirtied_pause
> ?
>
> The former will cause a drift in pause times due to truncation of the
> excess.

It should be fine in either way, as long as the "truncated" number is
passed to balance_dirty_pages():

+ balance_dirty_pages(mapping, current->nr_dirtied);
+ current->nr_dirtied = 0;

or

+ balance_dirty_pages(mapping, current->nr_dirtied_pause);
+ current->nr_dirtied -= current->nr_dirtied_pause;

Thanks,
Fengguang


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