[PATCH RFC v3 03/35] mm: page_alloc: Add an arch hook to filter MIGRATE_CMA allocations

[Alexandru Elisei]

As an architecture might have specific requirements around the allocation
of CMA pages, add an arch hook that can disable allocations from
MIGRATE_CMA, if the allocation was otherwise allowed.

This will be used by arm64, which will put tag storage pages on the
MIGRATE_CMA list, and tag storage pages cannot be tagged. The filter will
be used to deny using MIGRATE_CMA for __GFP_TAGGED allocations.

Signed-off-by: Alexandru Elisei <alexandru.elisei at arm.com>
---
 include/linux/pgtable.h | 7 +++++++
 mm/page_alloc.c         | 3 ++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 6d98d5fdd697..c5ddec6b5305 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -905,6 +905,13 @@ static inline void arch_do_swap_page(struct mm_struct *mm,
 static inline void arch_free_pages_prepare(struct page *page, int order) { }
 #endif
 
+#ifndef __HAVE_ARCH_ALLOC_CMA
+static inline bool arch_alloc_cma(gfp_t gfp)
+{
+	return true;
+}
+#endif
+
 #ifndef __HAVE_ARCH_UNMAP_ONE
 /*
  * Some architectures support metadata associated with a page. When a
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 27282a1c82fe..a96d47a6393e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3157,7 +3157,8 @@ static inline unsigned int gfp_to_alloc_flags_cma(gfp_t gfp_mask,
 						  unsigned int alloc_flags)
 {
 #ifdef CONFIG_CMA
-	if (gfp_migratetype(gfp_mask) == MIGRATE_MOVABLE)
+	if (gfp_migratetype(gfp_mask) == MIGRATE_MOVABLE &&
+	    arch_alloc_cma(gfp_mask))
 		alloc_flags |= ALLOC_CMA;
 #endif
 	return alloc_flags;
-- 
2.43.0