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


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