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

Peter Zijlstra
2012-03-19T17:28:45Z

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) {