Re: [PATCH v3] mm/page_alloc: fix freeing of MIGRATE_RESERVE migratetype pages
From: Vlastimil Babka
Date: Fri Mar 21 2014 - 10:16:47 EST
On 03/06/2014 06:35 PM, Bartlomiej Zolnierkiewicz wrote:
Pages allocated from MIGRATE_RESERVE migratetype pageblocks
are not freed back to MIGRATE_RESERVE migratetype free
lists in free_pcppages_bulk()->__free_one_page() if we got
to free_pcppages_bulk() through drain_[zone_]pages().
The freeing through free_hot_cold_page() is okay because
freepage migratetype is set to pageblock migratetype before
calling free_pcppages_bulk().
I think this is somewhat misleading and got me confused for a while.
It's not about the call path of free_pcppages_bulk(), but about the
fact that rmqueue_bulk() has been called at some point to fill up the
pcp lists, and had to resort to __rmqueue_fallback(). So, going through
free_hot_cold_page() might give you correct migratetype for the last
page freed, but the pcp lists may still contain misplaced pages from
earlier rmqueue_bulk().
If pages of MIGRATE_RESERVE
migratetype end up on the free lists of other migratetype
whole Reserved pageblock may be later changed to the other
migratetype in __rmqueue_fallback() and it will be never
changed back to be a Reserved pageblock. Fix the issue by
moving freepage migratetype setting from rmqueue_bulk() to
__rmqueue[_fallback]() and preserving freepage migratetype
as an original pageblock migratetype for MIGRATE_RESERVE
migratetype pages.
Actually wouldn't the easiest solution to this particular problem to
check current pageblock migratetype in try_to_steal_freepages() and
disallow changing it. However I agree that preventing the misplaced page
in the first place would be even better.
The problem was introduced in v2.6.31 by commit ed0ae21
("page allocator: do not call get_pageblock_migratetype()
more than necessary").
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
Reported-by: Yong-Taek Lee <ytk.lee@xxxxxxxxxxx>
Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
---
v2:
- updated patch description, there is no __zone_pcp_update()
in newer kernels
v3:
- set freepage migratetype in __rmqueue[_fallback]()
instead of rmqueue_bulk() (per Mel's request)
mm/page_alloc.c | 27 ++++++++++++++++++---------
1 file changed, 18 insertions(+), 9 deletions(-)
Index: b/mm/page_alloc.c
===================================================================
--- a/mm/page_alloc.c 2014-03-06 18:10:21.884422983 +0100
+++ b/mm/page_alloc.c 2014-03-06 18:10:27.016422895 +0100
@@ -1094,7 +1094,7 @@ __rmqueue_fallback(struct zone *zone, in
struct free_area *area;
int current_order;
struct page *page;
- int migratetype, new_type, i;
+ int migratetype, new_type, mt = start_migratetype, i;
A better naming would help, "mt" and "migratetype" are the same thing
and it gets too confusing.
/* Find the largest possible block of pages in the other list */
for (current_order = MAX_ORDER-1; current_order >= order;
@@ -1125,6 +1125,14 @@ __rmqueue_fallback(struct zone *zone, in
expand(zone, page, order, current_order, area,
new_type);
+ if (IS_ENABLED(CONFIG_CMA)) {
+ mt = get_pageblock_migratetype(page);
+ if (!is_migrate_cma(mt) &&
+ !is_migrate_isolate(mt))
+ mt = start_migratetype;
+ }
+ set_freepage_migratetype(page, mt);
+
trace_mm_page_alloc_extfrag(page, order, current_order,
start_migratetype, migratetype, new_type);
@@ -1147,7 +1155,9 @@ static struct page *__rmqueue(struct zon
retry_reserve:
page = __rmqueue_smallest(zone, order, migratetype);
- if (unlikely(!page) && migratetype != MIGRATE_RESERVE) {
+ if (likely(page)) {
+ set_freepage_migratetype(page, migratetype);
Are you sure that here the checking of of CMA and ISOLATE is not needed?
Did the original rmqueue_bulk() have this checking only for the
__rmqueue_fallback() case? Why wouldn't the check already be only in
__rmqueue_fallback() then?
+ } else if (migratetype != MIGRATE_RESERVE) {
page = __rmqueue_fallback(zone, order, migratetype);
/*
@@ -1174,7 +1184,7 @@ static int rmqueue_bulk(struct zone *zon
unsigned long count, struct list_head *list,
int migratetype, int cold)
{
- int mt = migratetype, i;
+ int i;
spin_lock(&zone->lock);
for (i = 0; i < count; ++i) {
@@ -1195,16 +1205,15 @@ static int rmqueue_bulk(struct zone *zon
list_add(&page->lru, list);
else
list_add_tail(&page->lru, list);
+ list = &page->lru;
if (IS_ENABLED(CONFIG_CMA)) {
- mt = get_pageblock_migratetype(page);
+ int mt = get_pageblock_migratetype(page);
if (!is_migrate_cma(mt) && !is_migrate_isolate(mt))
mt = migratetype;
+ if (is_migrate_cma(mt))
+ __mod_zone_page_state(zone, NR_FREE_CMA_PAGES,
+ -(1 << order));
}
- set_freepage_migratetype(page, mt);
- list = &page->lru;
- if (is_migrate_cma(mt))
- __mod_zone_page_state(zone, NR_FREE_CMA_PAGES,
- -(1 << order));
}
__mod_zone_page_state(zone, NR_FREE_PAGES, -(i << order));
spin_unlock(&zone->lock);
--
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