On 04/27/2015 09:23 AM, Joonsoo Kim wrote:
When we steal whole pageblock, we don't need to break highest order
freepage. Perhaps, there is small order freepage so we can use it.
This also gives us some code size reduction because expand() which
is used in __rmqueue_fallback() and inlined into __rmqueue_fallback()
is removed.
text data bss dec hex filename
37413 1440 624 39477 9a35 mm/page_alloc.o
37249 1440 624 39313 9991 mm/page_alloc.o
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
---
mm/page_alloc.c | 40 +++++++++++++++++++++-------------------
1 file changed, 21 insertions(+), 19 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ed0f1c6..044f16c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1239,14 +1239,14 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
}
/* Remove an element from the buddy allocator from the fallback list */
This is no longer accurate description.
-static inline struct page *
+static inline bool
__rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
{
struct free_area *area;
unsigned int current_order;
struct page *page;
int fallback_mt;
- bool can_steal;
+ bool can_steal_pageblock;
/* Find the largest possible block of pages in the other list */
for (current_order = MAX_ORDER-1;
@@ -1254,26 +1254,24 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
--current_order) {
area = &(zone->free_area[current_order]);
fallback_mt = find_suitable_fallback(area, current_order,
- start_migratetype, false, &can_steal);
+ start_migratetype, false,
+ &can_steal_pageblock);
if (fallback_mt == -1)
continue;
page = list_entry(area->free_list[fallback_mt].next,
struct page, lru);
- if (can_steal)
+ BUG_ON(!page);
Please no new BUG_ON. VM_BUG_ON maybe for debugging, otherwise just let
it panic on null pointer exception accessing page->lru later on.
+
+ if (can_steal_pageblock)
steal_suitable_fallback(zone, page, start_migratetype);
- /* Remove the page from the freelists */
- area->nr_free--;
- list_del(&page->lru);
- rmv_page_order(page);
+ list_move(&page->lru, &area->free_list[start_migratetype]);
This list_move is redundant if we are stealing whole pageblock, right?
Just put it in an else of the if above, and explain in comment?
- expand(zone, page, order, current_order, area,
- start_migratetype);
/*
* The freepage_migratetype may differ from pageblock's
* migratetype depending on the decisions in
- * try_to_steal_freepages(). This is OK as long as it
+ * find_suitable_fallback(). This is OK as long as it
* does not differ for MIGRATE_CMA pageblocks. For CMA
* we need to make sure unallocated pages flushed from
* pcp lists are returned to the correct freelist.
The whole thing with set_freepage_migratetype(page, start_migratetype);
below this comment is now redundant, as rmqueue_smallest will do it too.
The comment itself became outdated and misplaced too. I guess
MIGRATE_CMA is now handled just by the fact that is is not set as
fallback in the fallbacks array?
@@ -1283,10 +1281,10 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
trace_mm_page_alloc_extfrag(page, order, current_order,
start_migratetype, fallback_mt);
- return page;
+ return true;
}
- return NULL;
+ return false;
}
/*
@@ -1297,28 +1295,32 @@ static struct page *__rmqueue(struct zone *zone, unsigned int order,
int migratetype)
{
struct page *page;
+ bool steal_fallback;
-retry_reserve:
+retry:
page = __rmqueue_smallest(zone, order, migratetype);
if (unlikely(!page) && migratetype != MIGRATE_RESERVE) {
if (migratetype == MIGRATE_MOVABLE)
page = __rmqueue_cma_fallback(zone, order);
- if (!page)
- page = __rmqueue_fallback(zone, order, migratetype);
+ if (page)
+ goto out;
+
+ steal_fallback = __rmqueue_fallback(zone, order, migratetype);
/*
* Use MIGRATE_RESERVE rather than fail an allocation. goto
* is used because __rmqueue_smallest is an inline function
* and we want just one call site
*/
- if (!page) {
+ if (!steal_fallback)
migratetype = MIGRATE_RESERVE;
- goto retry_reserve;
- }
+
+ goto retry;
}
+out:
trace_mm_page_alloc_zone_locked(page, order, migratetype);
return page;
}
--
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