From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Subject: mm, page_alloc: defer debugging checks of pages allocated from the PCP
Every page allocated checks a number of page fields for validity. This
catches corruption bugs of pages that are already freed but it is
expensive. This patch weakens the debugging check by checking PCP pages
only when the PCP lists are being refilled. All compound pages are
checked. This potentially avoids debugging checks entirely if the PCP
lists are never emptied and refilled so some corruption issues may be
missed. Full checking requires DEBUG_VM.
With the two deferred debugging patches applied, the impact to a page
allocator microbenchmark is
4.6.0-rc3 4.6.0-rc3
inline-v3r6 deferalloc-v3r7
Min alloc-odr0-1 344.00 ( 0.00%) 317.00 ( 7.85%)
Min alloc-odr0-2 248.00 ( 0.00%) 231.00 ( 6.85%)
Min alloc-odr0-4 209.00 ( 0.00%) 192.00 ( 8.13%)
Min alloc-odr0-8 181.00 ( 0.00%) 166.00 ( 8.29%)
Min alloc-odr0-16 168.00 ( 0.00%) 154.00 ( 8.33%)
Min alloc-odr0-32 161.00 ( 0.00%) 148.00 ( 8.07%)
Min alloc-odr0-64 158.00 ( 0.00%) 145.00 ( 8.23%)
Min alloc-odr0-128 156.00 ( 0.00%) 143.00 ( 8.33%)
Min alloc-odr0-256 168.00 ( 0.00%) 154.00 ( 8.33%)
Min alloc-odr0-512 178.00 ( 0.00%) 167.00 ( 6.18%)
Min alloc-odr0-1024 186.00 ( 0.00%) 174.00 ( 6.45%)
Min alloc-odr0-2048 192.00 ( 0.00%) 180.00 ( 6.25%)
Min alloc-odr0-4096 198.00 ( 0.00%) 184.00 ( 7.07%)
Min alloc-odr0-8192 200.00 ( 0.00%) 188.00 ( 6.00%)
Min alloc-odr0-16384 201.00 ( 0.00%) 188.00 ( 6.47%)
Min free-odr0-1 189.00 ( 0.00%) 180.00 ( 4.76%)
Min free-odr0-2 132.00 ( 0.00%) 126.00 ( 4.55%)
Min free-odr0-4 104.00 ( 0.00%) 99.00 ( 4.81%)
Min free-odr0-8 90.00 ( 0.00%) 85.00 ( 5.56%)
Min free-odr0-16 84.00 ( 0.00%) 80.00 ( 4.76%)
Min free-odr0-32 80.00 ( 0.00%) 76.00 ( 5.00%)
Min free-odr0-64 78.00 ( 0.00%) 74.00 ( 5.13%)
Min free-odr0-128 77.00 ( 0.00%) 73.00 ( 5.19%)
Min free-odr0-256 94.00 ( 0.00%) 91.00 ( 3.19%)
Min free-odr0-512 108.00 ( 0.00%) 112.00 ( -3.70%)
Min free-odr0-1024 115.00 ( 0.00%) 118.00 ( -2.61%)
Min free-odr0-2048 120.00 ( 0.00%) 125.00 ( -4.17%)
Min free-odr0-4096 123.00 ( 0.00%) 129.00 ( -4.88%)
Min free-odr0-8192 126.00 ( 0.00%) 130.00 ( -3.17%)
Min free-odr0-16384 126.00 ( 0.00%) 131.00 ( -3.97%)
Note that the free paths for large numbers of pages is impacted as the
debugging cost gets shifted into that path when the page data is no longer
necessarily cache-hot.
Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 92 ++++++++++++++++++++++++++++++++--------------
1 file changed, 64 insertions(+), 28 deletions(-)
diff -puN mm/page_alloc.c~mm-page_alloc-defer-debugging-checks-of-pages-allocated-from-the-pcp mm/page_alloc.c
--- a/mm/page_alloc.c~mm-page_alloc-defer-debugging-checks-of-pages-allocated-from-the-pcp
+++ a/mm/page_alloc.c
@@ -1714,7 +1714,41 @@ static inline bool free_pages_prezeroed(
page_poisoning_enabled() && poisoned;
}
-static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
+#ifdef CONFIG_DEBUG_VM
+static bool check_pcp_refill(struct page *page)
+{
+ return false;
+}
+
+static bool check_new_pcp(struct page *page)
+{
+ return check_new_page(page);
+}
+#else
+static bool check_pcp_refill(struct page *page)
+{
+ return check_new_page(page);
+}
+static bool check_new_pcp(struct page *page)
+{
+ return false;
+}
+#endif /* CONFIG_DEBUG_VM */
+
+static bool check_new_pages(struct page *page, unsigned int order)
+{
+ int i;
+ for (i = 0; i < (1 << order); i++) {
+ struct page *p = page + i;
+
+ if (unlikely(check_new_page(p)))
+ return true;
+ }
+
+ return false;
+}
+
+static void prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
unsigned int alloc_flags)
{
int i;
@@ -1722,8 +1756,6 @@ static int prep_new_page(struct page *pa
for (i = 0; i < (1 << order); i++) {
struct page *p = page + i;
- if (unlikely(check_new_page(p)))
- return 1;
if (poisoned)
poisoned &= page_is_poisoned(p);
}
@@ -1755,8 +1787,6 @@ static int prep_new_page(struct page *pa
set_page_pfmemalloc(page);
else
clear_page_pfmemalloc(page);
-
- return 0;
}
/*
@@ -2178,6 +2208,9 @@ static int rmqueue_bulk(struct zone *zon
if (unlikely(page == NULL))
break;
+ if (unlikely(check_pcp_refill(page)))
+ continue;
+
/*
* Split buddy pages returned by expand() are received here
* in physical page order. The page is added to the callers and
@@ -2593,20 +2626,22 @@ struct page *buffered_rmqueue(struct zon
struct list_head *list;
local_irq_save(flags);
- pcp = &this_cpu_ptr(zone->pageset)->pcp;
- list = &pcp->lists[migratetype];
- if (list_empty(list)) {
- pcp->count += rmqueue_bulk(zone, 0,
- pcp->batch, list,
- migratetype, cold);
- if (unlikely(list_empty(list)))
- goto failed;
- }
+ do {
+ pcp = &this_cpu_ptr(zone->pageset)->pcp;
+ list = &pcp->lists[migratetype];
+ if (list_empty(list)) {
+ pcp->count += rmqueue_bulk(zone, 0,
+ pcp->batch, list,
+ migratetype, cold);
+ if (unlikely(list_empty(list)))
+ goto failed;
+ }
- if (cold)
- page = list_last_entry(list, struct page, lru);
- else
- page = list_first_entry(list, struct page, lru);
+ if (cold)
+ page = list_last_entry(list, struct page, lru);
+ else
+ page = list_first_entry(list, struct page, lru);
+ } while (page && check_new_pcp(page));
__dec_zone_state(zone, NR_ALLOC_BATCH);
list_del(&page->lru);
@@ -2619,14 +2654,16 @@ struct page *buffered_rmqueue(struct zon
WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1));
spin_lock_irqsave(&zone->lock, flags);
- page = NULL;
- if (alloc_flags & ALLOC_HARDER) {
- page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
- if (page)
- trace_mm_page_alloc_zone_locked(page, order, migratetype);
- }
- if (!page)
- page = __rmqueue(zone, order, migratetype);
+ do {
+ page = NULL;
+ if (alloc_flags & ALLOC_HARDER) {
+ page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
+ if (page)
+ trace_mm_page_alloc_zone_locked(page, order, migratetype);
+ }
+ if (!page)
+ page = __rmqueue(zone, order, migratetype);
+ } while (page && check_new_pages(page, order));
spin_unlock(&zone->lock);
if (!page)
goto failed;
@@ -2993,8 +3030,7 @@ try_this_zone:
page = buffered_rmqueue(ac->preferred_zoneref->zone, zone, order,
gfp_mask, alloc_flags, ac->migratetype);
if (page) {
- if (prep_new_page(page, order, gfp_mask, alloc_flags))
- goto try_this_zone;
+ prep_new_page(page, order, gfp_mask, alloc_flags);
/*
* If this is a high-order atomic allocation then check
_
--
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