[RFC PATCH v4 1/3] mm/filemap: add mempolicy support to the filemap layer

[Shivank Garg <shivankg@amd.com>]

From: Shivansh Dhiman <shivansh.dhiman@amd.com>

Add NUMA mempolicy support to the filemap allocation path by introducing
new APIs that take a mempolicy argument:
- filemap_grab_folio_mpol()
- filemap_alloc_folio_mpol()
- __filemap_get_folio_mpol()

These APIs allow callers to specify a NUMA policy during page cache
allocations, enabling fine-grained control over memory placement. This is
particularly needed by KVM when using guest-memfd memory backends, where
the guest memory needs to be allocated according to the NUMA policy
specified by VMM.

The existing non-mempolicy APIs remain unchanged and continue to use the
default allocation behavior.

Signed-off-by: Shivansh Dhiman <shivansh.dhiman@amd.com>
Signed-off-by: Shivank Garg <shivankg@amd.com>
---
 include/linux/pagemap.h | 40 ++++++++++++++++++++++++++++++++++++++++
 mm/filemap.c            | 30 +++++++++++++++++++++++++-----
 2 files changed, 65 insertions(+), 5 deletions(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 47bfc6b1b632..4ae7fa63cb26 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -662,15 +662,25 @@ static inline void *detach_page_private(struct page *page)
 
 #ifdef CONFIG_NUMA
 struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order);
+struct folio *filemap_alloc_folio_mpol_noprof(gfp_t gfp, unsigned int order,
+						struct mempolicy *mpol);
 #else
 static inline struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order)
 {
 	return folio_alloc_noprof(gfp, order);
 }
+static inline struct folio *filemap_alloc_folio_mpol_noprof(gfp_t gfp,
+						unsigned int order,
+						struct mempolicy *mpol)
+{
+	return filemap_alloc_folio_noprof(gfp, order);
+}
 #endif
 
 #define filemap_alloc_folio(...)				\
 	alloc_hooks(filemap_alloc_folio_noprof(__VA_ARGS__))
+#define filemap_alloc_folio_mpol(...)				\
+	alloc_hooks(filemap_alloc_folio_mpol_noprof(__VA_ARGS__))
 
 static inline struct page *__page_cache_alloc(gfp_t gfp)
 {
@@ -762,6 +772,8 @@ static inline fgf_t fgf_set_order(size_t size)
 void *filemap_get_entry(struct address_space *mapping, pgoff_t index);
 struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 		fgf_t fgp_flags, gfp_t gfp);
+struct folio *__filemap_get_folio_mpol(struct address_space *mapping,
+		pgoff_t index, fgf_t fgp_flags, gfp_t gfp, struct mempolicy *mpol);
 struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
 		fgf_t fgp_flags, gfp_t gfp);
 
@@ -820,6 +832,34 @@ static inline struct folio *filemap_grab_folio(struct address_space *mapping,
 			mapping_gfp_mask(mapping));
 }
 
+/**
+ * filemap_grab_folio_mpol - grab a folio from the page cache
+ * @mapping: The address space to search
+ * @index: The page index
+ * @mpol: The mempolicy to apply
+ *
+ * Same as filemap_grab_folio(), except that it allocates the folio using
+ * given memory policy.
+ *
+ * Return: A found or created folio. ERR_PTR(-ENOMEM) if no folio is found
+ * and failed to create a folio.
+ */
+#ifdef CONFIG_NUMA
+static inline struct folio *filemap_grab_folio_mpol(struct address_space *mapping,
+					pgoff_t index, struct mempolicy *mpol)
+{
+	return __filemap_get_folio_mpol(mapping, index,
+			FGP_LOCK | FGP_ACCESSED | FGP_CREAT,
+			mapping_gfp_mask(mapping), mpol);
+}
+#else
+static inline struct folio *filemap_grab_folio_mpol(struct address_space *mapping,
+					pgoff_t index, struct mempolicy *mpol)
+{
+	return filemap_grab_folio(mapping, index);
+}
+#endif /* CONFIG_NUMA */
+
 /**
  * find_get_page - find and get a page reference
  * @mapping: the address_space to search
diff --git a/mm/filemap.c b/mm/filemap.c
index 804d7365680c..c5ea32702774 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1001,8 +1001,13 @@ int filemap_add_folio(struct address_space *mapping, struct folio *folio,
 EXPORT_SYMBOL_GPL(filemap_add_folio);
 
 #ifdef CONFIG_NUMA
-struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order)
+struct folio *filemap_alloc_folio_mpol_noprof(gfp_t gfp, unsigned int order,
+			struct mempolicy *mpol)
 {
+	if (mpol)
+		return folio_alloc_mpol_noprof(gfp, order, mpol,
+				NO_INTERLEAVE_INDEX, numa_node_id());
+
 	int n;
 	struct folio *folio;
 
@@ -1018,6 +1023,12 @@ struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order)
 	}
 	return folio_alloc_noprof(gfp, order);
 }
+EXPORT_SYMBOL(filemap_alloc_folio_mpol_noprof);
+
+struct folio *filemap_alloc_folio_noprof(gfp_t gfp, unsigned int order)
+{
+	return filemap_alloc_folio_mpol_noprof(gfp, order, NULL);
+}
 EXPORT_SYMBOL(filemap_alloc_folio_noprof);
 #endif
 
@@ -1881,11 +1892,12 @@ void *filemap_get_entry(struct address_space *mapping, pgoff_t index)
 }
 
 /**
- * __filemap_get_folio - Find and get a reference to a folio.
+ * __filemap_get_folio_mpol - Find and get a reference to a folio.
  * @mapping: The address_space to search.
  * @index: The page index.
  * @fgp_flags: %FGP flags modify how the folio is returned.
  * @gfp: Memory allocation flags to use if %FGP_CREAT is specified.
+ * @mpol: The mempolicy to apply.
  *
  * Looks up the page cache entry at @mapping & @index.
  *
@@ -1896,8 +1908,8 @@ void *filemap_get_entry(struct address_space *mapping, pgoff_t index)
  *
  * Return: The found folio or an ERR_PTR() otherwise.
  */
-struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
-		fgf_t fgp_flags, gfp_t gfp)
+struct folio *__filemap_get_folio_mpol(struct address_space *mapping, pgoff_t index,
+		fgf_t fgp_flags, gfp_t gfp, struct mempolicy *mpol)
 {
 	struct folio *folio;
 
@@ -1967,7 +1979,7 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 			err = -ENOMEM;
 			if (order > min_order)
 				alloc_gfp |= __GFP_NORETRY | __GFP_NOWARN;
-			folio = filemap_alloc_folio(alloc_gfp, order);
+			folio = filemap_alloc_folio_mpol(alloc_gfp, order, mpol);
 			if (!folio)
 				continue;
 
@@ -2003,6 +2015,14 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
 		folio_clear_dropbehind(folio);
 	return folio;
 }
+EXPORT_SYMBOL(__filemap_get_folio_mpol);
+
+struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
+		fgf_t fgp_flags, gfp_t gfp)
+{
+	return __filemap_get_folio_mpol(mapping, index,
+			fgp_flags, gfp, NULL);
+}
 EXPORT_SYMBOL(__filemap_get_folio);
 
 static inline struct folio *find_get_entry(struct xa_state *xas, pgoff_t max,
-- 
2.34.1