mempolicy trivia: use pgoff_t in shared mempolicy tree

Prefer the more explicit "pgoff_t" to "unsigned long" when dealing with a
shared mempolicy tree.  Delete confusing comment about pseudo mm vmas.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Hugh Dickins <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Kefeng Wang <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Kravetz <[email protected]>
Cc: Nhat Pham <[email protected]>
Cc: Sidhartha Kumar <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Tejun heo <[email protected]>
Cc: Vishal Moola (Oracle) <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: Yosry Ahmed <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Hugh Dickins

include/linux/mempolicy.h

@@ -105,30 +105,24 @@ static inline bool mpol_equal(struct mempolicy *a, struct mempolicy *b)
 
 /*
  * Tree of shared policies for a shared memory region.
- * Maintain the policies in a pseudo mm that contains vmas. The vmas
- * carry the policy. As a special twist the pseudo mm is indexed in pages, not
- * bytes, so that we can work with shared memory segments bigger than
- * unsigned long.
  */
-
-struct sp_node {
-	struct rb_node nd;
-	unsigned long start, end;
-	struct mempolicy *policy;
-};
-
 struct shared_policy {
 	struct rb_root root;
 	rwlock_t lock;
 };
+struct sp_node {
+	struct rb_node nd;
+	pgoff_t start, end;
+	struct mempolicy *policy;
+};
 
 int vma_dup_policy(struct vm_area_struct *src, struct vm_area_struct *dst);
 void mpol_shared_policy_init(struct shared_policy *sp, struct mempolicy *mpol);
 int mpol_set_shared_policy(struct shared_policy *sp,
 			   struct vm_area_struct *vma, struct mempolicy *mpol);
 void mpol_free_shared_policy(struct shared_policy *sp);
 struct mempolicy *mpol_shared_policy_lookup(struct shared_policy *sp,
-					    unsigned long idx);
+					    pgoff_t idx);
 
 struct mempolicy *get_task_policy(struct task_struct *p);
 struct mempolicy *__get_vma_policy(struct vm_area_struct *vma,
@@ -214,7 +208,7 @@ static inline void mpol_free_shared_policy(struct shared_policy *sp)
 }
 
 static inline struct mempolicy *
-mpol_shared_policy_lookup(struct shared_policy *sp, unsigned long idx)
+mpol_shared_policy_lookup(struct shared_policy *sp, pgoff_t idx)
 {
 	return NULL;
 }

mm/mempolicy.c

@@ -2428,8 +2428,8 @@ bool __mpol_equal(struct mempolicy *a, struct mempolicy *b)
  * lookup first element intersecting start-end.  Caller holds sp->lock for
  * reading or for writing
  */
-static struct sp_node *
-sp_lookup(struct shared_policy *sp, unsigned long start, unsigned long end)
+static struct sp_node *sp_lookup(struct shared_policy *sp,
+					pgoff_t start, pgoff_t end)
 {
 	struct rb_node *n = sp->root.rb_node;
 
@@ -2483,8 +2483,8 @@ static void sp_insert(struct shared_policy *sp, struct sp_node *new)
 }
 
 /* Find shared policy intersecting idx */
-struct mempolicy *
-mpol_shared_policy_lookup(struct shared_policy *sp, unsigned long idx)
+struct mempolicy *mpol_shared_policy_lookup(struct shared_policy *sp,
+						pgoff_t idx)
 {
 	struct mempolicy *pol = NULL;
 	struct sp_node *sn;
@@ -2652,8 +2652,8 @@ static struct sp_node *sp_alloc(unsigned long start, unsigned long end,
 }
 
 /* Replace a policy range. */
-static int shared_policy_replace(struct shared_policy *sp, unsigned long start,
-				 unsigned long end, struct sp_node *new)
+static int shared_policy_replace(struct shared_policy *sp, pgoff_t start,
+				 pgoff_t end, struct sp_node *new)
 {
 	struct sp_node *n;
 	struct sp_node *n_new = NULL;