From bea904d54d6faa92400f10c8ea3d3828b8e1eb93 Mon Sep 17 00:00:00 2001 From: Lee Schermerhorn Date: Mon, 28 Apr 2008 02:13:18 -0700 Subject: mempolicy: use MPOL_PREFERRED for system-wide default policy 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//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 Cc: Christoph Lameter Cc: David Rientjes Cc: Mel Gorman Cc: Andi Kleen Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/mempolicy.c | 68 ++++++++++++++++++++++++++++++++++++---------------------- 1 file changed, 42 insertions(+), 26 deletions(-) (limited to 'mm') diff --git a/mm/mempolicy.c b/mm/mempolicy.c index a237295f819..fea4a5da6e4 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -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(¤t->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); -- cgit v1.2.3-70-g09d2