Re: [RFC][PATCH 10/26] mm, mpol: Make mempolicy home-node aware

[Peter Zijlstra <peterz@infradead.org>]

On Mon, 2012-03-19 at 18:09 +0100, Peter Zijlstra wrote:
> On Mon, 2012-03-19 at 10:31 -0500, Christoph Lameter wrote:
> 
> > MPOL_DEFAULT is a certain type of behavior right now that applications
> > rely on. If you change that then these applications will no longer work as
> > expected.
> > 
> > MPOL_DEFAULT is currently set to be the default policy on bootup. You can
> > change that of course and allow setting MPOL_DEFAULT manually for
> > applications that rely on old behavor. Instead set the default behavior on
> > bootup for MPOL_HOME_NODE.
> > 
> > So the default system behavior would be MPOL_HOME_NODE but it could be
> > overriding by numactl to allow old apps to run as they are used to run.
> 
> Ah, OK. Although that's a mightily confusing usage of the word DEFAULT.
> How about instead we make MPOL_LOCAL a real policy and allow explicitly
> setting that?

I suspect something like the below might suffice.. still need to test it
though.

---
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -21,6 +21,7 @@ enum {
 	MPOL_BIND,
 	MPOL_INTERLEAVE,
 	MPOL_NOOP,		/* retain existing policy for range */
+	MPOL_LOCAL,
 	MPOL_MAX,	/* always last member of enum */
 };
 
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -285,6 +285,10 @@ struct mempolicy *mpol_new(unsigned shor
 			     (flags & MPOL_F_RELATIVE_NODES)))
 				return ERR_PTR(-EINVAL);
 		}
+	} else if (mode == MPOL_LOCAL) {
+		if (!nodes_empty(*nodes))
+			return ERR_PTR(-EINVAL);
+		mode = MPOL_PREFERRED;
 	} else if (nodes_empty(*nodes))
 		return ERR_PTR(-EINVAL);
 	policy = kmem_cache_alloc(policy_cache, GFP_KERNEL | __GFP_ZERO);
@@ -2446,7 +2450,6 @@ void numa_default_policy(void)
  * "local" is pseudo-policy:  MPOL_PREFERRED with MPOL_F_LOCAL flag
  * Used only for mpol_parse_str() and mpol_to_str()
  */
-#define MPOL_LOCAL MPOL_MAX
 static const char * const policy_modes[] =
 {
 	[MPOL_DEFAULT]    = "default",
@@ -2499,12 +2502,12 @@ int mpol_parse_str(char *str, struct mem
 	if (flags)
 		*flags++ = '\0';	/* terminate mode string */
 
-	for (mode = 0; mode <= MPOL_LOCAL; mode++) {
+	for (mode = 0; mode < MPOL_MAX; mode++) {
 		if (!strcmp(str, policy_modes[mode])) {
 			break;
 		}
 	}
-	if (mode > MPOL_LOCAL)
+	if (mode >= MPOL_MAX)
 		goto out;
 
 	switch (mode) {

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