Re: [PATCH 16/27] mm, page_alloc: Consider dirtyable memory in terms of nodes

Johannes Weiner
2016-02-28T16:17:55Z

On Tue, Feb 23, 2016 at 03:17:55PM +0000, Mel Gorman wrote:
> @@ -686,6 +680,12 @@ typedef struct pglist_data {
> /* Number of pages migrated during the rate limiting time interval */
> unsigned long numabalancing_migrate_nr_pages;
> #endif
> + /*
> + * This is a per-zone reserve of pages that are not available
> + * to userspace allocations.
> + */
> + unsigned long totalreserve_pages;

"per-node reserve"

> @@ -297,22 +306,11 @@ static unsigned long highmem_dirtyable_memory(unsigned long total)
> int node;
> unsigned long x = 0;
>
> - for_each_node_state(node, N_HIGH_MEMORY) {
> - struct zone *z = &NODE_DATA(node)->node_zones[ZONE_HIGHMEM];
> -
> - x += zone_dirtyable_memory(z);
> - }
> /*
> - * Unreclaimable memory (kernel memory or anonymous memory
> - * without swap) can bring down the dirtyable pages below
> - * the zone's dirty balance reserve and the above calculation
> - * will underflow. However we still want to add in nodes
> - * which are below threshold (negative values) to get a more
> - * accurate calculation but make sure that the total never
> - * underflows.
> + * LRU lists are per-node so there is accurate way of accurately
> + * calculating dirtyable memory of just the high zone

"no accurate way of calculating"

> @@ -2665,7 +2665,7 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
> * will require awareness of zones in the
> * dirty-throttling and the flusher threads.
> */
> - if (ac->spread_dirty_pages && !zone_dirty_ok(zone))
> + if (ac->spread_dirty_pages && !node_dirty_ok(zone->zone_pgdat))
> continue;

The comment above this branch can be updated. I'm attaching a diff
below, feel free to use it.

> mark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
> @@ -6333,7 +6333,7 @@ static void calculate_totalreserve_pages(void)
> if (max > zone->managed_pages)
> max = zone->managed_pages;
>
> - zone->totalreserve_pages = max;
> + pgdat->totalreserve_pages += max;

calculate_totalreserve_pages() can be called repeatedly. It needs to
be set freshly in this function, not added to.

---

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c461a94..fedd0b5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2596,28 +2596,21 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
continue;
/*
* When allocating a page cache page for writing, we
- * want to get it from a zone that is within its dirty
- * limit, such that no single zone holds more than its
+ * want to get it from a node that is within its dirty
+ * limit, such that no node zone holds more than its
* proportional share of globally allowed dirty pages.
- * The dirty limits take into account the zone's
+ * The dirty limits take into account the node's
* lowmem reserves and high watermark so that kswapd
* should be able to balance it without having to
* write pages from its LRU list.
*
- * This may look like it could increase pressure on
- * lower zones by failing allocations in higher zones
- * before they are full. But the pages that do spill
- * over are limited as the lower zones are protected
- * by this very same mechanism. It should not become
- * a practical burden to them.
- *
* XXX: For now, allow allocations to potentially
- * exceed the per-zone dirty limit in the slowpath
+ * exceed the per-node dirty limit in the slowpath
* (spread_dirty_pages unset) before going into reclaim,
* which is important when on a NUMA setup the allowed
- * zones are together not big enough to reach the
+ * nodes are together not big enough to reach the
* global limit. The proper fix for these situations
- * will require awareness of zones in the
+ * will require awareness of nodes in the
* dirty-throttling and the flusher threads.
*/
if (ac->spread_dirty_pages) {