mempolicy: document {set|get}_policy() vm_ops APIs
Document mempolicy return value reference semantics assumed by the rest of the
mempolicy code for the set_ and get_policy vm_ops in <linux/mm.h>--where the
prototypes are defined--to inform any future mempolicy vm_op writers what the
rest of the subsystem expects of them.
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/mm.h b/include/linux/mm.h
index bc0ad24..8b7f4a5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -172,7 +172,25 @@
* writable, if an error is returned it will cause a SIGBUS */
int (*page_mkwrite)(struct vm_area_struct *vma, struct page *page);
#ifdef CONFIG_NUMA
+ /*
+ * set_policy() op must add a reference to any non-NULL @new mempolicy
+ * to hold the policy upon return. Caller should pass NULL @new to
+ * remove a policy and fall back to surrounding context--i.e. do not
+ * install a MPOL_DEFAULT policy, nor the task or system default
+ * mempolicy.
+ */
int (*set_policy)(struct vm_area_struct *vma, struct mempolicy *new);
+
+ /*
+ * get_policy() op must add reference [mpol_get()] to any policy at
+ * (vma,addr) marked as MPOL_SHARED. The shared policy infrastructure
+ * in mm/mempolicy.c will do this automatically.
+ * get_policy() must NOT add a ref if the policy at (vma,addr) is not
+ * marked as MPOL_SHARED. vma policies are protected by the mmap_sem.
+ * If no [shared/vma] mempolicy exists at the addr, get_policy() op
+ * must return NULL--i.e., do not "fallback" to task or system default
+ * policy.
+ */
struct mempolicy *(*get_policy)(struct vm_area_struct *vma,
unsigned long addr);
int (*migrate)(struct vm_area_struct *vma, const nodemask_t *from,
