Subject: [PATCH v3 1/2] mm/cma: provide option to opt out from exposing pages on activation failure

From: Hari Bathini <[email-masked]>
Date: Mon, 17 Jan 2022 13:22:45 +0530

Commit 072355c1cf2d ("mm/cma: expose all pages to the buddy if
activation of an area fails") started exposing all pages to buddy
allocator on CMA activation failure. But there can be CMA users that
want to handle the reserved memory differently on CMA allocation
failure. Provide an option to opt out from exposing pages to buddy
for such cases.

Signed-off-by: Hari Bathini <[email-masked]>
Reviewed-by: David Hildenbrand <[email-masked]>
---

Changes in v3:
* Dropped NULL check in cma_reserve_pages_on_error().
* Dropped explicit initialization of cma->reserve_pages_on_error to
  'false' in cma_init_reserved_mem().
* Added Reviewed-by tag from David.

Changes in v2:
* Changed cma->free_pages_on_error to cma->reserve_pages_on_error and
  cma_dont_free_pages_on_error() to cma_reserve_pages_on_error() to
  avoid confusion.

 include/linux/cma.h |  2 ++
 mm/cma.c            | 11 +++++++++--
 mm/cma.h            |  1 +
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/linux/cma.h b/include/linux/cma.h
index bd801023504b..51d540eee18a 100644
--- a/include/linux/cma.h
+++ b/include/linux/cma.h
@@ -50,4 +50,6 @@ extern bool cma_pages_valid(struct cma *cma, const struct page *pages, unsigned
 extern bool cma_release(struct cma *cma, const struct page *pages, unsigned long count);
 
 extern int cma_for_each_area(int (*it)(struct cma *cma, void *data), void *data);
+
+extern void cma_reserve_pages_on_error(struct cma *cma);
 #endif
diff --git a/mm/cma.c b/mm/cma.c
index bc9ca8f3c487..766f1b82b532 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -131,8 +131,10 @@ static void __init cma_activate_area(struct cma *cma)
 	bitmap_free(cma->bitmap);
 out_error:
 	/* Expose all pages to the buddy, they are useless for CMA. */
-	for (pfn = base_pfn; pfn < base_pfn + cma->count; pfn++)
-		free_reserved_page(pfn_to_page(pfn));
+	if (!cma->reserve_pages_on_error) {
+		for (pfn = base_pfn; pfn < base_pfn + cma->count; pfn++)
+			free_reserved_page(pfn_to_page(pfn));
+	}
 	totalcma_pages -= cma->count;
 	cma->count = 0;
 	pr_err("CMA area %s could not be activated\n", cma->name);
@@ -150,6 +152,11 @@ static int __init cma_init_reserved_areas(void)
 }
 core_initcall(cma_init_reserved_areas);
 
+void __init cma_reserve_pages_on_error(struct cma *cma)
+{
+	cma->reserve_pages_on_error = true;
+}
+
 /**
  * cma_init_reserved_mem() - create custom contiguous area from reserved memory
  * @base: Base address of the reserved area
diff --git a/mm/cma.h b/mm/cma.h
index 2c775877eae2..88a0595670b7 100644
--- a/mm/cma.h
+++ b/mm/cma.h
@@ -30,6 +30,7 @@ struct cma {
 	/* kobject requires dynamic object */
 	struct cma_kobject *cma_kobj;
 #endif
+	bool reserve_pages_on_error;
 };
 
 extern struct cma cma_areas[MAX_CMA_AREAS];
-- 
2.34.1