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@@ -147,6 +147,24 @@ static struct prop_descriptor vm_completions;
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* clamping level.
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*/
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+/*
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+ * In a memory zone, there is a certain amount of pages we consider
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+ * available for the page cache, which is essentially the number of
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+ * free and reclaimable pages, minus some zone reserves to protect
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+ * lowmem and the ability to uphold the zone's watermarks without
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+ * requiring writeback.
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+ *
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+ * This number of dirtyable pages is the base value of which the
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+ * user-configurable dirty ratio is the effictive number of pages that
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+ * are allowed to be actually dirtied. Per individual zone, or
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+ * globally by using the sum of dirtyable pages over all zones.
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+ *
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+ * Because the user is allowed to specify the dirty limit globally as
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+ * absolute number of bytes, calculating the per-zone dirty limit can
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+ * require translating the configured limit into a percentage of
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+ * global dirtyable memory first.
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+ */
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+
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static unsigned long highmem_dirtyable_memory(unsigned long total)
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{
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#ifdef CONFIG_HIGHMEM
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@@ -232,6 +250,70 @@ void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
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trace_global_dirty_state(background, dirty);
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}
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+/**
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+ * zone_dirtyable_memory - number of dirtyable pages in a zone
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+ * @zone: the zone
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+ *
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+ * Returns the zone's number of pages potentially available for dirty
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+ * page cache. This is the base value for the per-zone dirty limits.
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+ */
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+static unsigned long zone_dirtyable_memory(struct zone *zone)
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+{
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+ /*
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+ * The effective global number of dirtyable pages may exclude
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+ * highmem as a big-picture measure to keep the ratio between
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+ * dirty memory and lowmem reasonable.
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+ *
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+ * But this function is purely about the individual zone and a
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+ * highmem zone can hold its share of dirty pages, so we don't
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+ * care about vm_highmem_is_dirtyable here.
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+ */
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+ return zone_page_state(zone, NR_FREE_PAGES) +
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+ zone_reclaimable_pages(zone) -
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+ zone->dirty_balance_reserve;
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+}
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+
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+/**
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+ * zone_dirty_limit - maximum number of dirty pages allowed in a zone
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+ * @zone: the zone
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+ *
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+ * Returns the maximum number of dirty pages allowed in a zone, based
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+ * on the zone's dirtyable memory.
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+ */
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+static unsigned long zone_dirty_limit(struct zone *zone)
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+{
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+ unsigned long zone_memory = zone_dirtyable_memory(zone);
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+ struct task_struct *tsk = current;
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+ unsigned long dirty;
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+
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+ if (vm_dirty_bytes)
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+ dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE) *
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+ zone_memory / global_dirtyable_memory();
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+ else
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+ dirty = vm_dirty_ratio * zone_memory / 100;
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+
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+ if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk))
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+ dirty += dirty / 4;
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+
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+ return dirty;
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+}
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+
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+/**
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+ * zone_dirty_ok - tells whether a zone is within its dirty limits
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+ * @zone: the zone to check
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+ *
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+ * Returns %true when the dirty pages in @zone are within the zone's
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+ * dirty limit, %false if the limit is exceeded.
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+ */
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+bool zone_dirty_ok(struct zone *zone)
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+{
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+ unsigned long limit = zone_dirty_limit(zone);
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+
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+ return zone_page_state(zone, NR_FILE_DIRTY) +
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+ zone_page_state(zone, NR_UNSTABLE_NFS) +
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+ zone_page_state(zone, NR_WRITEBACK) <= limit;
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+}
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+
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/*
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* couple the period to the dirty_ratio:
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*
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Johannes Weiner