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Subject[PATCH v4 1/7] mm: page_alloc: avoid merging non-fallbackable pageblocks with others.
Date
From: Zi Yan <ziy@nvidia.com>

This is done in addition to MIGRATE_ISOLATE pageblock merge avoidance.
It prepares for the upcoming removal of the MAX_ORDER-1 alignment
requirement for CMA and alloc_contig_range().

MIGRARTE_HIGHATOMIC should not merge with other migratetypes like
MIGRATE_ISOLATE and MIGRARTE_CMA[1], so this commit prevents that too.
Also add MIGRARTE_HIGHATOMIC to fallbacks array for completeness.

[1] https://lore.kernel.org/linux-mm/20211130100853.GP3366@techsingularity.net/

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
include/linux/mmzone.h | 11 +++++++++++
mm/page_alloc.c | 37 ++++++++++++++++++++-----------------
2 files changed, 31 insertions(+), 17 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index aed44e9b5d89..71b77aab748d 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -83,6 +83,17 @@ static inline bool is_migrate_movable(int mt)
return is_migrate_cma(mt) || mt == MIGRATE_MOVABLE;
}

+/*
+ * Check whether a migratetype can be merged with another migratetype.
+ *
+ * It is only mergeable when it can fall back to other migratetypes for
+ * allocation. See fallbacks[MIGRATE_TYPES][3] in page_alloc.c.
+ */
+static inline bool migratetype_is_mergeable(int mt)
+{
+ return mt < MIGRATE_PCPTYPES;
+}
+
#define for_each_migratetype_order(order, type) \
for (order = 0; order < MAX_ORDER; order++) \
for (type = 0; type < MIGRATE_TYPES; type++)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8dd6399bafb5..15de65215c02 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1117,25 +1117,24 @@ static inline void __free_one_page(struct page *page,
}
if (order < MAX_ORDER - 1) {
/* If we are here, it means order is >= pageblock_order.
- * We want to prevent merge between freepages on isolate
- * pageblock and normal pageblock. Without this, pageblock
- * isolation could cause incorrect freepage or CMA accounting.
+ * We want to prevent merge between freepages on pageblock
+ * without fallbacks and normal pageblock. Without this,
+ * pageblock isolation could cause incorrect freepage or CMA
+ * accounting or HIGHATOMIC accounting.
*
* We don't want to hit this code for the more frequent
* low-order merging.
*/
- if (unlikely(has_isolate_pageblock(zone))) {
- int buddy_mt;
+ int buddy_mt;

- buddy_pfn = __find_buddy_pfn(pfn, order);
- buddy = page + (buddy_pfn - pfn);
- buddy_mt = get_pageblock_migratetype(buddy);
+ buddy_pfn = __find_buddy_pfn(pfn, order);
+ buddy = page + (buddy_pfn - pfn);
+ buddy_mt = get_pageblock_migratetype(buddy);

- if (migratetype != buddy_mt
- && (is_migrate_isolate(migratetype) ||
- is_migrate_isolate(buddy_mt)))
- goto done_merging;
- }
+ if (migratetype != buddy_mt
+ && (!migratetype_is_mergeable(migratetype) ||
+ !migratetype_is_mergeable(buddy_mt)))
+ goto done_merging;
max_order = order + 1;
goto continue_merging;
}
@@ -2484,6 +2483,7 @@ static int fallbacks[MIGRATE_TYPES][3] = {
[MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE, MIGRATE_TYPES },
[MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_TYPES },
[MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE, MIGRATE_TYPES },
+ [MIGRATE_HIGHATOMIC] = { MIGRATE_TYPES }, /* Never used */
#ifdef CONFIG_CMA
[MIGRATE_CMA] = { MIGRATE_TYPES }, /* Never used */
#endif
@@ -2795,8 +2795,8 @@ static void reserve_highatomic_pageblock(struct page *page, struct zone *zone,

/* Yoink! */
mt = get_pageblock_migratetype(page);
- if (!is_migrate_highatomic(mt) && !is_migrate_isolate(mt)
- && !is_migrate_cma(mt)) {
+ /* Only reserve normal pageblocks (i.e., they can merge with others) */
+ if (migratetype_is_mergeable(mt)) {
zone->nr_reserved_highatomic += pageblock_nr_pages;
set_pageblock_migratetype(page, MIGRATE_HIGHATOMIC);
move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, NULL);
@@ -3545,8 +3545,11 @@ int __isolate_free_page(struct page *page, unsigned int order)
struct page *endpage = page + (1 << order) - 1;
for (; page < endpage; page += pageblock_nr_pages) {
int mt = get_pageblock_migratetype(page);
- if (!is_migrate_isolate(mt) && !is_migrate_cma(mt)
- && !is_migrate_highatomic(mt))
+ /*
+ * Only change normal pageblocks (i.e., they can merge
+ * with others)
+ */
+ if (migratetype_is_mergeable(mt))
set_pageblock_migratetype(page,
MIGRATE_MOVABLE);
}
--
2.34.1
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