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mempolicy: use MPOL_PREFERRED for system-wide default policy

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Currently, when one specifies MPOL_DEFAULT via a NUMA memory policy API
[set_mempolicy(), mbind() and internal versions], the kernel simply installs a
NULL struct mempolicy pointer in the appropriate context: task policy, vma
policy, or shared policy.  This causes any use of that policy to "fall back"
to the next most specific policy scope.

The only use of MPOL_DEFAULT to mean "local allocation" is in the system
default policy.  This requires extra checks/cases for MPOL_DEFAULT in many
mempolicy.c functions.

There is another, "preferred" way to specify local allocation via the APIs.
That is using the MPOL_PREFERRED policy mode with an empty nodemask.
Internally, the empty nodemask gets converted to a preferred_node id of '-1'.
All internal usage of MPOL_PREFERRED will convert the '-1' to the id of the
node local to the cpu where the allocation occurs.

System default policy, except during boot, is hard-coded to "local
allocation".  By using the MPOL_PREFERRED mode with a negative value of
preferred node for system default policy, MPOL_DEFAULT will never occur in the
'policy' member of a struct mempolicy.  Thus, we can remove all checks for
MPOL_DEFAULT when converting policy to a node id/zonelist in the allocation
paths.

In slab_node() return local node id when policy pointer is NULL.  No need to
set a pol value to take the switch default.  Replace switch default with
BUG()--i.e., shouldn't happen.

With this patch MPOL_DEFAULT is only used in the APIs, including internal
calls to do_set_mempolicy() and in the display of policy in
/proc/<pid>/numa_maps.  It always means "fall back" to the the next most
specific policy scope.  This simplifies the description of memory policies
quite a bit, with no visible change in behavior.

get_mempolicy() continues to return MPOL_DEFAULT and an empty nodemask when
the requested policy [task or vma/shared] is NULL.  These are the values one
would supply via set_mempolicy() or mbind() to achieve that condition--default
behavior.

This patch updates Documentation to reflect this change.

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>
This commit is contained in:
Lee Schermerhorn
2008-04-28 02:13:18 -07:00
committed by Linus Torvalds
parent 52cd3b0740
commit bea904d54d
2 changed files with 58 additions and 60 deletions
Download Patch File Download Diff File Expand all files Collapse all files

68
mm/mempolicy.c
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@@ -104,9 +104,13 @@ static struct kmem_cache *sn_cache;
policied. */
enum zone_type policy_zone = 0;
/*
* run-time system-wide default policy => local allocation
*/
struct mempolicy default_policy = {
.refcnt = ATOMIC_INIT(1), /* never free it */
.mode = MPOL_DEFAULT,
.mode = MPOL_PREFERRED,
.v = { .preferred_node = -1 },
};
static const struct mempolicy_operations {
@@ -189,7 +193,7 @@ static struct mempolicy *mpol_new(unsigned short mode, unsigned short flags,
if (mode == MPOL_DEFAULT) {
if (nodes && !nodes_empty(*nodes))
return ERR_PTR(-EINVAL);
return NULL;
return NULL; /* simply delete any existing policy */
}
VM_BUG_ON(!nodes);
@@ -246,7 +250,6 @@ void __mpol_put(struct mempolicy *p)
{
if (!atomic_dec_and_test(&p->refcnt))
return;
p->mode = MPOL_DEFAULT;
kmem_cache_free(policy_cache, p);
}
@@ -626,13 +629,16 @@ static long do_set_mempolicy(unsigned short mode, unsigned short flags,
return 0;
}
/* Fill a zone bitmap for a policy */
static void get_zonemask(struct mempolicy *p, nodemask_t *nodes)
/*
* Return nodemask for policy for get_mempolicy() query
*/
static void get_policy_nodemask(struct mempolicy *p, nodemask_t *nodes)
{
nodes_clear(*nodes);
if (p == &default_policy)
return;
switch (p->mode) {
case MPOL_DEFAULT:
break;
case MPOL_BIND:
/* Fall through */
case MPOL_INTERLEAVE:
@@ -686,6 +692,11 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
}
if (flags & MPOL_F_ADDR) {
/*
* Do NOT fall back to task policy if the
* vma/shared policy at addr is NULL. We
* want to return MPOL_DEFAULT in this case.
*/
down_read(&mm->mmap_sem);
vma = find_vma_intersection(mm, addr, addr+1);
if (!vma) {
@@ -700,7 +711,7 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
return -EINVAL;
if (!pol)
pol = &default_policy;
pol = &default_policy; /* indicates default behavior */
if (flags & MPOL_F_NODE) {
if (flags & MPOL_F_ADDR) {
@@ -715,8 +726,11 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
err = -EINVAL;
goto out;
}
} else
*policy = pol->mode | pol->flags;
} else {
*policy = pol == &default_policy ? MPOL_DEFAULT :
pol->mode;
*policy |= pol->flags;
}
if (vma) {
up_read(&current->mm->mmap_sem);
@@ -725,7 +739,7 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
err = 0;
if (nmask)
get_zonemask(pol, nmask);
get_policy_nodemask(pol, nmask);
out:
mpol_cond_put(pol);
@@ -1286,8 +1300,7 @@ static struct mempolicy *get_vma_policy(struct task_struct *task,
addr);
if (vpol)
pol = vpol;
} else if (vma->vm_policy &&
vma->vm_policy->mode != MPOL_DEFAULT)
} else if (vma->vm_policy)
pol = vma->vm_policy;
}
if (!pol)
@@ -1334,7 +1347,6 @@ static struct zonelist *policy_zonelist(gfp_t gfp, struct mempolicy *policy)
nd = first_node(policy->v.nodes);
break;
case MPOL_INTERLEAVE: /* should not happen */
case MPOL_DEFAULT:
nd = numa_node_id();
break;
default:
@@ -1369,9 +1381,15 @@ static unsigned interleave_nodes(struct mempolicy *policy)
*/
unsigned slab_node(struct mempolicy *policy)
{
unsigned short pol = policy ? policy->mode : MPOL_DEFAULT;
if (!policy)
return numa_node_id();
switch (policy->mode) {
case MPOL_PREFERRED:
if (unlikely(policy->v.preferred_node >= 0))
return policy->v.preferred_node;
return numa_node_id();
switch (pol) {
case MPOL_INTERLEAVE:
return interleave_nodes(policy);
@@ -1390,13 +1408,8 @@ unsigned slab_node(struct mempolicy *policy)
return zone->node;
}
case MPOL_PREFERRED:
if (policy->v.preferred_node >= 0)
return policy->v.preferred_node;
/* Fall through */
default:
return numa_node_id();
BUG();
}
}
@@ -1650,8 +1663,6 @@ int __mpol_equal(struct mempolicy *a, struct mempolicy *b)
if (a->mode != MPOL_DEFAULT && !mpol_match_intent(a, b))
return 0;
switch (a->mode) {
case MPOL_DEFAULT:
return 1;
case MPOL_BIND:
/* Fall through */
case MPOL_INTERLEAVE:
@@ -1828,7 +1839,7 @@ void mpol_shared_policy_init(struct shared_policy *info, unsigned short policy,
if (policy != MPOL_DEFAULT) {
struct mempolicy *newpol;
/* Falls back to MPOL_DEFAULT on any error */
/* Falls back to NULL policy [MPOL_DEFAULT] on any error */
newpol = mpol_new(policy, flags, policy_nodes);
if (!IS_ERR(newpol)) {
/* Create pseudo-vma that contains just the policy */
@@ -1952,9 +1963,14 @@ static inline int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
char *p = buffer;
int l;
nodemask_t nodes;
unsigned short mode = pol ? pol->mode : MPOL_DEFAULT;
unsigned short mode;
unsigned short flags = pol ? pol->flags : 0;
if (!pol || pol == &default_policy)
mode = MPOL_DEFAULT;
else
mode = pol->mode;
switch (mode) {
case MPOL_DEFAULT:
nodes_clear(nodes);