Re: [PATCH 4/5] writeback: per task dirty rate limit

Wu Fengguang
2011-08-10T03:30:05Z

On Wed, Aug 10, 2011 at 01:46:21AM +0800, Vivek Goyal wrote:
> On Sat, Aug 06, 2011 at 04:44:51PM +0800, Wu Fengguang wrote:
>
> [..]
> > * balance_dirty_pages() must be called by processes which are generating dirty
> > * data. It looks at the number of dirty pages in the machine and will force
> > * the caller to perform writeback if the system is over `vm_dirty_ratio'.
> > @@ -1008,6 +1005,9 @@ static void balance_dirty_pages(struct a
> > if (clear_dirty_exceeded && bdi->dirty_exceeded)
> > bdi->dirty_exceeded = 0;
> >
> > + current->nr_dirtied = 0;
> > + current->nr_dirtied_pause = ratelimit_pages(nr_dirty, dirty_thresh);
> > +
> > if (writeback_in_progress(bdi))
> > return;
> >
> > @@ -1034,8 +1034,6 @@ void set_page_dirty_balance(struct page
> > }
> > }
> >
> > -static DEFINE_PER_CPU(unsigned long, bdp_ratelimits) = 0;
> > -
> > /**
> > * balance_dirty_pages_ratelimited_nr - balance dirty memory state
> > * @mapping: address_space which was dirtied
> > @@ -1055,30 +1053,17 @@ void balance_dirty_pages_ratelimited_nr(
> > {
> > struct backing_dev_info *bdi = mapping->backing_dev_info;
> > unsigned long ratelimit;
> > - unsigned long *p;
> >
> > if (!bdi_cap_account_dirty(bdi))
> > return;
> >
> > - ratelimit = ratelimit_pages;
> > - if (mapping->backing_dev_info->dirty_exceeded)
> > + ratelimit = current->nr_dirtied_pause;
> > + if (bdi->dirty_exceeded)
> > ratelimit = 8;
>
> Should we make sure that ratelimit is more than 8? It could be that
> ratelimit is 1 and we set it higher (just reverse of what we wanted?)

Good catch! I actually just fixed it in that direction :)

if (bdi->dirty_exceeded)
- ratelimit = 8;
+ ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));

Thanks,
Fengguang