[PATCH mm-unstable] mm: introduce folio_is_pfmemalloc

[Sidhartha Kumar]

Add a folio equivalent for page_is_pfmemalloc. This removes two instances
of page_is_pfmemalloc(folio_page(folio, 0)) so the folio can be used
directly.

Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
---
 include/linux/mm.h | 15 +++++++++++++++
 mm/slab.c          |  2 +-
 mm/slub.c          |  2 +-
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c37f9330f14e..79d5a0cbf4c3 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1906,6 +1906,21 @@ static inline bool page_is_pfmemalloc(const struct page *page)
 	return (uintptr_t)page->lru.next & BIT(1);
 }
 
+/*
+ * Return true only if the folio has been allocated with
+ * ALLOC_NO_WATERMARKS and the low watermark was not
+ * met implying that the system is under some pressure.
+ */
+static inline bool folio_is_pfmemalloc(const struct folio *folio)
+{
+	/*
+	 * lru.next has bit 1 set if the page is allocated from the
+	 * pfmemalloc reserves.  Callers may simply overwrite it if
+	 * they do not need to preserve that information.
+	 */
+	return (uintptr_t)folio->lru.next & BIT(1);
+}
+
 /*
  * Only to be called by the page allocator on a freshly allocated
  * page.
diff --git a/mm/slab.c b/mm/slab.c
index 7a269db050ee..01291ecbc0d8 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1373,7 +1373,7 @@ static struct slab *kmem_getpages(struct kmem_cache *cachep, gfp_t flags,
 	/* Make the flag visible before any changes to folio->mapping */
 	smp_wmb();
 	/* Record if ALLOC_NO_WATERMARKS was set when allocating the slab */
-	if (sk_memalloc_socks() && page_is_pfmemalloc(folio_page(folio, 0)))
+	if (sk_memalloc_socks() && folio_is_pfmemalloc(folio))
 		slab_set_pfmemalloc(slab);
 
 	return slab;
diff --git a/mm/slub.c b/mm/slub.c
index 13459c69095a..0cbe6eff23fa 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1859,7 +1859,7 @@ static inline struct slab *alloc_slab_page(gfp_t flags, int node,
 	__folio_set_slab(folio);
 	/* Make the flag visible before any changes to folio->mapping */
 	smp_wmb();
-	if (page_is_pfmemalloc(folio_page(folio, 0)))
+	if (folio_is_pfmemalloc(folio))
 		slab_set_pfmemalloc(slab);
 
 	return slab;
-- 
2.39.0