After "no_merge for order 0", the biggest overhead in free path for
order 0 pages is now add_to_cluster(). As pages are freed one by one,
it caused frequent operation of add_to_cluster().
Ideally, if only one migratetype pcp list has pages to free and
count=pcp->batch in free_pcppages_bulk(), we can avoid calling
add_to_cluster() one time per page but adding them in one go as
a single cluster so this patch just did this.
This optimization brings zone->lock contention down from 25% to
almost zero again using the parallel free workload.
Signed-off-by: Aaron Lu <aaron...@intel.com>
---
mm/page_alloc.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 46 insertions(+), 3 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e60a248030dc..204696f6c2f4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1242,6 +1242,36 @@ static inline void prefetch_buddy(struct page *page)
prefetch(buddy);
}
+static inline bool free_cluster_pages(struct zone *zone, struct list_head
*list,
+ int mt, int count)
+{
+ struct cluster *c;
+ struct page *page, *n;
+
+ if (!can_skip_merge(zone, 0))
+ return false;
+
+ if (count != this_cpu_ptr(zone->pageset)->pcp.batch)
+ return false;
+
+ c = new_cluster(zone, count, list_first_entry(list, struct page, lru));
+ if (unlikely(!c))
+ return false;
+
+ list_for_each_entry_safe(page, n, list, lru) {
+ set_page_order(page, 0);
+ set_page_merge_skipped(page);
+ page->cluster = c;
+ list_add(&page->lru, &zone->free_area[0].free_list[mt]);
+ }
+
+ INIT_LIST_HEAD(list);
+ zone->free_area[0].nr_free += count;
+ __mod_zone_page_state(zone, NR_FREE_PAGES, count);
+
+ return true;
+}
+
/*
* Frees a number of pages from the PCP lists
* Assumes all pages on list are in same zone, and of same order.
@@ -1256,10 +1286,10 @@ static inline void prefetch_buddy(struct page *page)
static void free_pcppages_bulk(struct zone *zone, int count,
struct per_cpu_pages *pcp)
{
- int migratetype = 0;
- int batch_free = 0;
+ int migratetype = 0, i, count_mt[MIGRATE_PCPTYPES] = {0};
+ int batch_free = 0, saved_count = count;
int prefetch_nr = 0;
- bool isolated_pageblocks;
+ bool isolated_pageblocks, single_mt = false;
struct page *page, *tmp;
LIST_HEAD(head);
@@ -1283,6 +1313,7 @@ static void free_pcppages_bulk(struct zone *zone, int
count,
/* This is the only non-empty list. Free them all. */
if (batch_free == MIGRATE_PCPTYPES)
batch_free = count;
+ count_mt[migratetype] += batch_free;
do {
page = list_last_entry(list, struct page, lru);
@@ -1314,12 +1345,24 @@ static void free_pcppages_bulk(struct zone *zone, int
count,
} while (--count && --batch_free && !list_empty(list));
}
+ for (i = 0; i < MIGRATE_PCPTYPES; i++) {
+ if (count_mt[i] == saved_count) {
+ single_mt = true;
+ break;
+ }
+ }
+
spin_lock(&zone->lock);
isolated_pageblocks = has_isolate_pageblock(zone);
+ if (!isolated_pageblocks && single_mt)
+ free_cluster_pages(zone, &head, migratetype, saved_count);
+
/*
* Use safe version since after __free_one_page(),
* page->lru.next will not point to original list.
+ *
+ * If free_cluster_pages() succeeds, head will be an empty list here.
*/
list_for_each_entry_safe(page, tmp, &head, lru) {
int mt = get_pcppage_migratetype(page);
--
2.17.2
