[PATCH v2 1/3] mm: page_alloc: add a watermark check that knows the migratetype

["Kiryl Shutsemau (Meta)" <kas@kernel.org>]

The high-order check in __zone_watermark_ok() accepts a free page of any
migratetype.  Under ALLOC_NOFRAGMENT, a request below pageblock_order can
only take a page of its own migratetype or claim a whole free block, so
the check can pass when the allocation cannot succeed.

Telling those apart needs the request's migratetype, but not every check
wants them told apart.  A check whether an allocation can be served now
has to count only the pages it can take.

A check whether there is enough free memory counts every migratetype:
kswapd and kcompactd balancing a zone, order-0 thresholds, the
slowpath's forecast whether reclaim and compaction can still make
progress.  Reclaim and compaction work across migratetypes to free whole
pageblocks.

Move the body of __zone_watermark_ok() into __zone_watermark_ok_mt(),
which takes the migratetype as well, and make __zone_watermark_ok() a
wrapper around it for the second kind of check.  These use the new
function:

  - the allocator fast path, zone_watermark_fast();
  - its recheck after node reclaim in get_page_from_freelist();
  - compaction's up-front check, compaction_suit_allocation_order().

Declare both in mm/internal.h: nothing outside mm uses them.

Nothing reads the migratetype yet: no functional change.

Tested-by: Dev Jain <dev.jain@arm.com>
Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
---
 include/linux/mmzone.h |  3 ---
 mm/compaction.c        | 11 ++++++-----
 mm/internal.h          |  7 +++++++
 mm/page_alloc.c        | 37 ++++++++++++++++++++++++++++---------
 4 files changed, 41 insertions(+), 17 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index ecd1ebd49756..4d9347a399fa 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1637,9 +1637,6 @@ static inline unsigned long pgdat_end_pfn(pg_data_t *pgdat)
 #include <linux/memory_hotplug.h>
 
 void build_all_zonelists(pg_data_t *pgdat);
-bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
-			 int highest_zoneidx, unsigned int alloc_flags,
-			 long free_pages);
 bool zone_watermark_ok(struct zone *z, unsigned int order,
 		unsigned long mark, int highest_zoneidx,
 		unsigned int alloc_flags);
diff --git a/mm/compaction.c b/mm/compaction.c
index f1b2060eb201..6c553d0e90f8 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2520,7 +2520,7 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
 static enum compact_result
 compaction_suit_allocation_order(struct zone *zone, unsigned int order,
 				 int highest_zoneidx, unsigned int alloc_flags,
-				 bool async, bool kcompactd)
+				 int migratetype, bool async, bool kcompactd)
 {
 	unsigned long free_pages;
 	unsigned long watermark;
@@ -2531,8 +2531,8 @@ compaction_suit_allocation_order(struct zone *zone, unsigned int order,
 		free_pages = zone_page_state(zone, NR_FREE_PAGES);
 
 	watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
-	if (__zone_watermark_ok(zone, order, watermark, highest_zoneidx,
-				alloc_flags, free_pages))
+	if (__zone_watermark_ok_mt(zone, order, watermark, highest_zoneidx,
+				   alloc_flags, free_pages, migratetype))
 		return COMPACT_SUCCESS;
 
 	/*
@@ -2588,6 +2588,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
 		ret = compaction_suit_allocation_order(cc->zone, cc->order,
 						       cc->highest_zoneidx,
 						       cc->alloc_flags,
+						       cc->migratetype,
 						       cc->mode == MIGRATE_ASYNC,
 						       !cc->direct_compaction);
 		if (ret != COMPACT_CONTINUE)
@@ -3073,7 +3074,7 @@ static bool kcompactd_node_suitable(pg_data_t *pgdat)
 		ret = compaction_suit_allocation_order(zone,
 				pgdat->kcompactd_max_order,
 				highest_zoneidx, alloc_flags,
-				false, true);
+				MIGRATE_MOVABLE, false, true);
 		if (ret == COMPACT_CONTINUE)
 			return true;
 	}
@@ -3116,7 +3117,7 @@ static void kcompactd_do_work(pg_data_t *pgdat)
 
 		ret = compaction_suit_allocation_order(zone,
 				cc.order, zoneid, cc.alloc_flags,
-				false, true);
+				MIGRATE_MOVABLE, false, true);
 		if (ret != COMPACT_CONTINUE)
 			continue;
 
diff --git a/mm/internal.h b/mm/internal.h
index 566cbd2dce48..8e58e2db5e09 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -726,6 +726,13 @@ extern int min_free_kbytes;
 extern int defrag_mode;
 
 void setup_per_zone_wmarks(void);
+bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
+			 int highest_zoneidx, unsigned int alloc_flags,
+			 long free_pages);
+bool __zone_watermark_ok_mt(struct zone *z, unsigned int order,
+			    unsigned long mark, int highest_zoneidx,
+			    unsigned int alloc_flags, long free_pages,
+			    int migratetype);
 void calculate_min_free_kbytes(void);
 int __meminit init_per_zone_wmark_min(void);
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a8cac5e01066..7730660bdd09 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3587,9 +3587,10 @@ static inline long __zone_watermark_unusable_free(struct zone *z,
  * one free page of a suitable size. Checking now avoids taking the zone lock
  * to check in the allocation paths if no pages are free.
  */
-bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
-			 int highest_zoneidx, unsigned int alloc_flags,
-			 long free_pages)
+bool __zone_watermark_ok_mt(struct zone *z, unsigned int order,
+			    unsigned long mark, int highest_zoneidx,
+			    unsigned int alloc_flags, long free_pages,
+			    int migratetype)
 {
 	long min = mark;
 	int o;
@@ -3665,6 +3666,21 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
 	return false;
 }
 
+/*
+ * For checks that are not about serving one allocation now: kswapd and
+ * kcompactd balancing a zone, order-0 thresholds, forecasts whether
+ * reclaim and compaction can still make progress.  They count free pages
+ * of every migratetype: reclaim and compaction work across migratetypes
+ * to free whole pageblocks.
+ */
+bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
+			 int highest_zoneidx, unsigned int alloc_flags,
+			 long free_pages)
+{
+	return __zone_watermark_ok_mt(z, order, mark, highest_zoneidx,
+				      alloc_flags, free_pages, MIGRATE_MOVABLE);
+}
+
 bool zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
 		      int highest_zoneidx, unsigned int alloc_flags)
 {
@@ -3697,8 +3713,8 @@ static inline bool zone_watermark_fast(struct zone *z, unsigned int order,
 			return true;
 	}
 
-	if (__zone_watermark_ok(z, order, mark, highest_zoneidx, alloc_flags,
-					free_pages))
+	if (__zone_watermark_ok_mt(z, order, mark, highest_zoneidx, alloc_flags,
+				   free_pages, gfp_migratetype(gfp_mask)))
 		return true;
 
 	/*
@@ -3710,8 +3726,9 @@ static inline bool zone_watermark_fast(struct zone *z, unsigned int order,
 	if (unlikely(!order && (alloc_flags & ALLOC_MIN_RESERVE) && z->watermark_boost
 		&& ((alloc_flags & ALLOC_WMARK_MASK) == WMARK_MIN))) {
 		mark = z->_watermark[WMARK_MIN];
-		return __zone_watermark_ok(z, order, mark, highest_zoneidx,
-					alloc_flags, free_pages);
+		return __zone_watermark_ok_mt(z, order, mark, highest_zoneidx,
+					      alloc_flags, free_pages,
+					      gfp_migratetype(gfp_mask));
 	}
 
 	return false;
@@ -3923,8 +3940,10 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
 				continue;
 
 			/* did we reclaim enough */
-			if (!zone_watermark_ok(zone, order, mark,
-					       ac->highest_zoneidx, alloc_flags))
+			if (!__zone_watermark_ok_mt(zone, order, mark,
+					ac->highest_zoneidx, alloc_flags,
+					zone_page_state(zone, NR_FREE_PAGES),
+					gfp_migratetype(gfp_mask)))
 				continue;
 		}
 
-- 
2.54.0