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    SubjectRe: [patch 4/5] mm: writeback: throttle __GFP_WRITE on per-zone dirty limits
    On Mon 25-07-11 22:19:18, Johannes Weiner wrote:
    [...]
    > diff --git a/mm/page-writeback.c b/mm/page-writeback.c
    > index 41dc871..ce673ec 100644
    > --- a/mm/page-writeback.c
    > +++ b/mm/page-writeback.c
    > @@ -378,6 +390,24 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
    > }
    > EXPORT_SYMBOL(bdi_set_max_ratio);
    >
    > +static void sanitize_dirty_limits(unsigned long *pbackground,
    > + unsigned long *pdirty)
    > +{
    > + unsigned long background = *pbackground;
    > + unsigned long dirty = *pdirty;
    > + struct task_struct *tsk;
    > +
    > + if (background >= dirty)
    > + background = dirty / 2;
    > + tsk = current;
    > + if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
    > + background += background / 4;
    > + dirty += dirty / 4;
    > + }
    > + *pbackground = background;
    > + *pdirty = dirty;
    > +}
    > +
    > /*
    > * global_dirty_limits - background-writeback and dirty-throttling thresholds
    > *
    > @@ -389,33 +419,52 @@ EXPORT_SYMBOL(bdi_set_max_ratio);
    > */
    > void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
    > {
    > - unsigned long background;
    > - unsigned long dirty;
    > unsigned long uninitialized_var(available_memory);
    > - struct task_struct *tsk;
    >
    > if (!vm_dirty_bytes || !dirty_background_bytes)
    > available_memory = determine_dirtyable_memory();
    >
    > if (vm_dirty_bytes)
    > - dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
    > + *pdirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
    > else
    > - dirty = (vm_dirty_ratio * available_memory) / 100;
    > + *pdirty = vm_dirty_ratio * available_memory / 100;
    >
    > if (dirty_background_bytes)
    > - background = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
    > + *pbackground = DIV_ROUND_UP(dirty_background_bytes, PAGE_SIZE);
    > else
    > - background = (dirty_background_ratio * available_memory) / 100;
    > + *pbackground = dirty_background_ratio * available_memory / 100;
    >
    > - if (background >= dirty)
    > - background = dirty / 2;
    > - tsk = current;
    > - if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
    > - background += background / 4;
    > - dirty += dirty / 4;
    > - }
    > - *pbackground = background;
    > - *pdirty = dirty;
    > + sanitize_dirty_limits(pbackground, pdirty);
    > +}

    Hmm, wouldn't be the patch little bit easier to read if this was
    outside in a separate (cleanup) one?

    --
    Michal Hocko
    SUSE Labs
    SUSE LINUX s.r.o.
    Lihovarska 1060/12
    190 00 Praha 9
    Czech Republic


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