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    SubjectRe: [patch 2/2] mm: add dirty_background_bytes and dirty_bytes sysctls
    On Sun, 23 Nov 2008 10:55:16 -0800 (PST)
    David Rientjes <rientjes@google.com> wrote:

    > This change introduces two new sysctls to /proc/sys/vm:
    > dirty_background_bytes and dirty_bytes.
    >
    >
    > ...
    >
    > @@ -365,23 +429,29 @@ void
    > get_dirty_limits(unsigned long *pbackground, unsigned long *pdirty,
    > unsigned long *pbdi_dirty, struct backing_dev_info *bdi)
    > {
    > - int background_ratio; /* Percentages */
    > - int dirty_ratio;
    > unsigned long background;
    > unsigned long dirty;
    > unsigned long available_memory = determine_dirtyable_memory();
    > struct task_struct *tsk;
    >
    > - dirty_ratio = vm_dirty_ratio;
    > - if (dirty_ratio < 5)
    > - dirty_ratio = 5;
    > + if (vm_dirty_bytes)
    > + dirty = (vm_dirty_bytes + PAGE_SIZE) / PAGE_SIZE;

    It would be conventional to use DIV_ROUND_UP() here.

    > + else {
    > + int dirty_ratio;

    hm, I wonder why vm_dirty_ratio has a signed type.

    > - background_ratio = dirty_background_ratio;
    > - if (background_ratio >= dirty_ratio)
    > - background_ratio = dirty_ratio / 2;
    > + dirty_ratio = vm_dirty_ratio;
    > + if (dirty_ratio < 5)
    > + dirty_ratio = 5;
    > + dirty = (dirty_ratio * available_memory) / 100;
    > + }
    > +
    > + if (dirty_background_bytes)
    > + background = (dirty_background_bytes + PAGE_SIZE) / PAGE_SIZE;

    DIV_ROUND_UP()?

    > + else
    > + background = (dirty_background_ratio * available_memory) / 100;
    >
    > - background = (background_ratio * available_memory) / 100;
    > - dirty = (dirty_ratio * available_memory) / 100;
    > + if (background >= dirty)
    > + background = dirty / 2;
    > tsk = current;
    > if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) {
    > background += background / 4;


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