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Subject[PATCH/RFC] mm: do not regard CMA pages as free on watermark check
__zone_watermark_ok() does not corrrectly take high-order
CMA pageblocks into account: high-order CMA blocks are not
removed from the watermark check. Moreover, CMA pageblocks
may suddenly vanish through CMA allocation, so let's not
regard these pages as free in __zone_watermark_ok().

This patch also adds some primitive testing for the method
implemented which has proven that it works as it should.

Signed-off-by: Vitaly Wool <vitalywool@gmail.com>
---
include/linux/mmzone.h | 1 +
mm/page_alloc.c | 56 +++++++++++++++++++++++++++++++++++++++++++++-----
mm/page_isolation.c | 2 +-
3 files changed, 53 insertions(+), 6 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index ac00e20..73268f5 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -92,6 +92,7 @@ static inline int get_pfnblock_migratetype(struct page *page, unsigned long pfn)
struct free_area {
struct list_head free_list[MIGRATE_TYPES];
unsigned long nr_free;
+ unsigned long nr_free_cma;
};

struct pglist_data;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5b5240b..69fbc93 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -672,6 +672,8 @@ static inline void __free_one_page(struct page *page,
} else {
list_del(&buddy->lru);
zone->free_area[order].nr_free--;
+ if (is_migrate_cma(migratetype))
+ zone->free_area[order].nr_free_cma--;
rmv_page_order(buddy);
}
combined_idx = buddy_idx & page_idx;
@@ -705,6 +707,8 @@ static inline void __free_one_page(struct page *page,
list_add(&page->lru, &zone->free_area[order].free_list[migratetype]);
out:
zone->free_area[order].nr_free++;
+ if (is_migrate_cma(migratetype))
+ zone->free_area[order].nr_free_cma++;
}

static inline int free_pages_check(struct page *page)
@@ -1278,6 +1282,8 @@ static inline void expand(struct zone *zone, struct page *page,
}
list_add(&page[size].lru, &area->free_list[migratetype]);
area->nr_free++;
+ if (is_migrate_cma(migratetype))
+ area->nr_free_cma++;
set_page_order(&page[size], high);
}
}
@@ -1379,6 +1385,8 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
list_del(&page->lru);
rmv_page_order(page);
area->nr_free--;
+ if (is_migrate_cma(migratetype))
+ area->nr_free_cma--;
expand(zone, page, order, current_order, area, migratetype);
set_freepage_migratetype(page, migratetype);
return page;
@@ -1428,6 +1436,7 @@ int move_freepages(struct zone *zone,
struct page *page;
unsigned long order;
int pages_moved = 0;
+ int mt;

#ifndef CONFIG_HOLES_IN_ZONE
/*
@@ -1457,7 +1466,12 @@ int move_freepages(struct zone *zone,
order = page_order(page);
list_move(&page->lru,
&zone->free_area[order].free_list[migratetype]);
+ mt = get_pageblock_migratetype(page);
+ if (is_migrate_cma(mt))
+ zone->free_area[order].nr_free_cma--;
set_freepage_migratetype(page, migratetype);
+ if (is_migrate_cma(migratetype))
+ zone->free_area[order].nr_free_cma++;
page += 1 << order;
pages_moved += 1 << order;
}
@@ -1621,6 +1635,8 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)

/* Remove the page from the freelists */
area->nr_free--;
+ if (unlikely(is_migrate_cma(start_migratetype)))
+ area->nr_free_cma--;
list_del(&page->lru);
rmv_page_order(page);

@@ -2012,6 +2028,8 @@ int __isolate_free_page(struct page *page, unsigned int order)
/* Remove page from free list */
list_del(&page->lru);
zone->free_area[order].nr_free--;
+ if (is_migrate_cma(mt))
+ zone->free_area[order].nr_free_cma--;
rmv_page_order(page);

set_page_owner(page, order, __GFP_MOVABLE);
@@ -2220,7 +2238,6 @@ static bool __zone_watermark_ok(struct zone *z, unsigned int order,
/* free_pages may go negative - that's OK */
long min = mark;
int o;
- long free_cma = 0;

free_pages -= (1 << order) - 1;
if (alloc_flags & ALLOC_HIGH)
@@ -2228,17 +2245,43 @@ static bool __zone_watermark_ok(struct zone *z, unsigned int order,
if (alloc_flags & ALLOC_HARDER)
min -= min / 4;
#ifdef CONFIG_CMA
- /* If allocation can't use CMA areas don't use free CMA pages */
+ /*
+ * We don't want to regard the pages on CMA region as free
+ * on watermark checking, since they cannot be used for
+ * unmovable/reclaimable allocation and they can suddenly
+ * vanish through CMA allocation
+ */
if (!(alloc_flags & ALLOC_CMA))
- free_cma = zone_page_state(z, NR_FREE_CMA_PAGES);
+ free_pages -= zone_page_state(z, NR_FREE_CMA_PAGES);
+#ifdef CONFIG_DEBUG_PAGEALLOC
+ {
+ long nr_free_cma;
+ for (o = 0, nr_free_cma = 0; o < MAX_ORDER; o++)
+ nr_free_cma += z->free_area[o].nr_free_cma << o;
+
+ /* nr_free_cma is a bit more realtime than zone_page_state
+ * and may thus differ from it a little, and it's ok
+ */
+ if (abs(nr_free_cma -
+ zone_page_state(z, NR_FREE_CMA_PAGES)) > 256)
+ pr_info_ratelimited("%s: nr_free_cma %ld instead of %ld\n",
+ __func__,
+ nr_free_cma,
+ zone_page_state(z, NR_FREE_CMA_PAGES));
+ }

--
Vitaly Wool <vitalywool@gmail.com>


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