[PATCH RFC 10/37] mm: compaction: Do not use MIGRATE_METADATA to replace pages with metadata

[Alexandru Elisei <alexandru.elisei@arm.com>]

MIGRATE_METADATA pages are special because for the one architecture
(arm64) that use them, it is not possible to have metadata associated
with a page used to store metadata.

To avoid a situation where a page with metadata is being migrated to a
page which cannot have metadata, keep track of whether such pages have
been isolated as the source for migration. When allocating a destination
page for migration, deny allocations from MIGRATE_METADATA if that's the
case.

fast_isolate_freepages() takes pages only from the MIGRATE_MOVABLE list,
which means it is not necessary to have a similar check, as
MIGRATE_METADATA pages will never be considered.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
---
 arch/arm64/include/asm/memory_metadata.h |  5 +++++
 include/asm-generic/memory_metadata.h    |  5 +++++
 include/linux/mmzone.h                   |  2 +-
 mm/compaction.c                          | 19 +++++++++++++++++--
 mm/internal.h                            |  1 +
 5 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/memory_metadata.h b/arch/arm64/include/asm/memory_metadata.h
index 5269be7f455f..c57c435c8ba3 100644
--- a/arch/arm64/include/asm/memory_metadata.h
+++ b/arch/arm64/include/asm/memory_metadata.h
@@ -7,6 +7,8 @@
 
 #include <asm-generic/memory_metadata.h>
 
+#include <asm/mte.h>
+
 #ifdef CONFIG_MEMORY_METADATA
 static inline bool metadata_storage_enabled(void)
 {
@@ -16,6 +18,9 @@ static inline bool alloc_can_use_metadata_pages(gfp_t gfp_mask)
 {
 	return false;
 }
+
+#define page_has_metadata(page)			page_mte_tagged(page)
+
 #endif /* CONFIG_MEMORY_METADATA */
 
 #endif /* __ASM_MEMORY_METADATA_H  */
diff --git a/include/asm-generic/memory_metadata.h b/include/asm-generic/memory_metadata.h
index 63ea661b354d..02b279823920 100644
--- a/include/asm-generic/memory_metadata.h
+++ b/include/asm-generic/memory_metadata.h
@@ -3,6 +3,7 @@
 #define __ASM_GENERIC_MEMORY_METADATA_H
 
 #include <linux/gfp.h>
+#include <linux/mm_types.h>
 
 extern unsigned long totalmetadata_pages;
 
@@ -15,6 +16,10 @@ static inline bool alloc_can_use_metadata_pages(gfp_t gfp_mask)
 {
 	return false;
 }
+static inline bool page_has_metadata(struct page *page)
+{
+	return false;
+}
 #endif /* !CONFIG_MEMORY_METADATA */
 
 #endif /* __ASM_GENERIC_MEMORY_METADATA_H */
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 48c237248d87..12d5072668ab 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -91,7 +91,7 @@ extern const char * const migratetype_names[MIGRATE_TYPES];
 
 static inline bool is_migrate_movable(int mt)
 {
-	return is_migrate_cma(mt) || mt == MIGRATE_MOVABLE;
+	return is_migrate_cma(mt) || is_migrate_metadata(mt) || mt == MIGRATE_MOVABLE;
 }
 
 /*
diff --git a/mm/compaction.c b/mm/compaction.c
index a29db409c5cc..cc0139fa0cb0 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1153,6 +1153,9 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 		nr_isolated += folio_nr_pages(folio);
 		nr_scanned += folio_nr_pages(folio) - 1;
 
+		if (page_has_metadata(&folio->page))
+			cc->source_has_metadata = true;
+
 		/*
 		 * Avoid isolating too much unless this block is being
 		 * fully scanned (e.g. dirty/writeback pages, parallel allocation)
@@ -1328,6 +1331,15 @@ static bool suitable_migration_source(struct compact_control *cc,
 static bool suitable_migration_target(struct compact_control *cc,
 							struct page *page)
 {
+	int block_mt;
+
+	block_mt = get_pageblock_migratetype(page);
+
+	/* Pages from MIGRATE_METADATA cannot have metadata. */
+	if (is_migrate_metadata(block_mt) && cc->source_has_metadata)
+		return false;
+
+
 	/* If the page is a large free page, then disallow migration */
 	if (PageBuddy(page)) {
 		/*
@@ -1342,8 +1354,11 @@ static bool suitable_migration_target(struct compact_control *cc,
 	if (cc->ignore_block_suitable)
 		return true;
 
-	/* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
-	if (is_migrate_movable(get_pageblock_migratetype(page)))
+	/*
+	 * If the block is MIGRATE_MOVABLE, MIGRATE_CMA or MIGRATE_METADATA,
+	 * allow migration.
+	 */
+	if (is_migrate_movable(block_mt))
 		return true;
 
 	/* Otherwise skip the block */
diff --git a/mm/internal.h b/mm/internal.h
index efd52c9f1578..d28ac0085f61 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -491,6 +491,7 @@ struct compact_control {
 					 * ensure forward progress.
 					 */
 	bool alloc_contig;		/* alloc_contig_range allocation */
+	bool source_has_metadata;	/* source pages have associated metadata */
 };
 
 /*
-- 
2.41.0