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Subject[PATCH] CMA: Fix CMA's page number is substructed twice in __zone_watermark_ok
Date
The original of this patch [1] is used to fix the issue in Joonsoo's CMA patch
"CMA: always treat free cma pages as non-free on watermark checking" [2].

Joonsoo reminded me that this issue affect current kernel too. So made a new
one for upstream.

Function __zone_watermark_ok substruct CMA pages number from free_pages
if system allocation can't use CMA areas:
/* If allocation can't use CMA areas don't use free CMA pages */
if (!(alloc_flags & ALLOC_CMA))
free_cma = zone_page_state(z, NR_FREE_CMA_PAGES);

But after this part of code
for (o = 0; o < order; o++) {
/* At the next order, this order's pages become unavailable */
free_pages -= z->free_area[o].nr_free << o;
CMA memory in each order is part of z->free_area[o].nr_free, then the CMA
page number of this order is substructed twice. This bug will make
__zone_watermark_ok return more false.

This patch add cma_free_area to struct free_area that just record the number
of CMA pages. And add it back in the order loop to handle the substruct
twice issue.

[1] https://lkml.org/lkml/2014/12/25/43
[2] https://lkml.org/lkml/2014/5/28/110

Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>
Signed-off-by: Weixing Liu <liuweixing@xiaomi.com>
---
include/linux/mmzone.h | 3 +++
mm/page_alloc.c | 22 ++++++++++++++++++++++
2 files changed, 25 insertions(+)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 2f0856d..094476b 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -92,6 +92,9 @@ 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;
+#ifdef CONFIG_CMA
+ unsigned long cma_nr_free;
+#endif
};

struct pglist_data;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7633c50..026cf27 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -650,6 +650,8 @@ 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].cma_nr_free--;
rmv_page_order(buddy);
}
combined_idx = buddy_idx & page_idx;
@@ -683,6 +685,8 @@ 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].cma_nr_free++;
}

static inline int free_pages_check(struct page *page)
@@ -937,6 +941,8 @@ 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->cma_nr_free++;
set_page_order(&page[size], high);
}
}
@@ -1020,6 +1026,8 @@ 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->cma_nr_free--;
expand(zone, page, order, current_order, area, migratetype);
set_freepage_migratetype(page, migratetype);
return page;
@@ -1208,6 +1216,8 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
page = list_entry(area->free_list[migratetype].next,
struct page, lru);
area->nr_free--;
+ if (is_migrate_cma(migratetype))
+ area->cma_nr_free--;

new_type = try_to_steal_freepages(zone, page,
start_migratetype,
@@ -1597,6 +1607,8 @@ 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].cma_nr_free--;
rmv_page_order(page);

/* Set the pageblock if the isolated page is at least a pageblock */
@@ -1827,6 +1839,13 @@ static bool __zone_watermark_ok(struct zone *z, unsigned int order,
/* At the next order, this order's pages become unavailable */
free_pages -= z->free_area[o].nr_free << o;

+ /* If CMA's page number of this order was substructed as part
+ of "zone_page_state(z, NR_FREE_CMA_PAGES)", subtracting
+ "z->free_area[o].nr_free << o" substructed CMA's page
+ number of this order again. So add it back. */
+ if (IS_ENABLED(CONFIG_CMA) && free_cma)
+ free_pages += z->free_area[o].cma_nr_free << o;
+
/* Require fewer higher order pages to be free */
min >>= 1;

@@ -4238,6 +4257,7 @@ static void __meminit zone_init_free_lists(struct zone *zone)
for_each_migratetype_order(order, t) {
INIT_LIST_HEAD(&zone->free_area[order].free_list[t]);
zone->free_area[order].nr_free = 0;
+ zone->free_area[order].cma_nr_free = 0;
}
}

@@ -6610,6 +6630,8 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
list_del(&page->lru);
rmv_page_order(page);
zone->free_area[order].nr_free--;
+ if (is_migrate_cma(get_pageblock_migratetype(page)))
+ zone->free_area[order].cma_nr_free--;
for (i = 0; i < (1 << order); i++)
SetPageReserved((page+i));
pfn += (1 << order);
--
1.9.1


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