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/<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
Linus Torvalds
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52cd3b0740
Коммит
bea904d54d
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@ -147,35 +147,18 @@ Components of Memory Policies
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Linux memory policy supports the following 4 behavioral modes:
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Default Mode--MPOL_DEFAULT: The behavior specified by this mode is
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context or scope dependent.
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Default Mode--MPOL_DEFAULT: This mode is only used in the memory
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policy APIs. Internally, MPOL_DEFAULT is converted to the NULL
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memory policy in all policy scopes. Any existing non-default policy
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will simply be removed when MPOL_DEFAULT is specified. As a result,
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MPOL_DEFAULT means "fall back to the next most specific policy scope."
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As mentioned in the Policy Scope section above, during normal
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system operation, the System Default Policy is hard coded to
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contain the Default mode.
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For example, a NULL or default task policy will fall back to the
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system default policy. A NULL or default vma policy will fall
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back to the task policy.
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In this context, default mode means "local" allocation--that is
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attempt to allocate the page from the node associated with the cpu
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where the fault occurs. If the "local" node has no memory, or the
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node's memory can be exhausted [no free pages available], local
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allocation will "fallback to"--attempt to allocate pages from--
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"nearby" nodes, in order of increasing "distance".
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Implementation detail -- subject to change: "Fallback" uses
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a per node list of sibling nodes--called zonelists--built at
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boot time, or when nodes or memory are added or removed from
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the system [memory hotplug]. These per node zonelist are
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constructed with nodes in order of increasing distance based
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on information provided by the platform firmware.
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When a task/process policy or a shared policy contains the Default
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mode, this also means "local allocation", as described above.
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In the context of a VMA, Default mode means "fall back to task
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policy"--which may or may not specify Default mode. Thus, Default
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mode can not be counted on to mean local allocation when used
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on a non-shared region of the address space. However, see
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MPOL_PREFERRED below.
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When specified in one of the memory policy APIs, the Default mode
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does not use the optional set of nodes.
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It is an error for the set of nodes specified for this policy to
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be non-empty.
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@ -187,19 +170,18 @@ Components of Memory Policies
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MPOL_PREFERRED: This mode specifies that the allocation should be
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attempted from the single node specified in the policy. If that
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allocation fails, the kernel will search other nodes, exactly as
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it would for a local allocation that started at the preferred node
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in increasing distance from the preferred node. "Local" allocation
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policy can be viewed as a Preferred policy that starts at the node
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allocation fails, the kernel will search other nodes, in order of
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increasing distance from the preferred node based on information
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provided by the platform firmware.
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containing the cpu where the allocation takes place.
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Internally, the Preferred policy uses a single node--the
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preferred_node member of struct mempolicy. A "distinguished
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value of this preferred_node, currently '-1', is interpreted
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as "the node containing the cpu where the allocation takes
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place"--local allocation. This is the way to specify
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local allocation for a specific range of addresses--i.e. for
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VMA policies.
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place"--local allocation. "Local" allocation policy can be
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viewed as a Preferred policy that starts at the node containing
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the cpu where the allocation takes place.
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It is possible for the user to specify that local allocation is
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always preferred by passing an empty nodemask with this mode.
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@ -104,9 +104,13 @@ static struct kmem_cache *sn_cache;
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policied. */
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enum zone_type policy_zone = 0;
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/*
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* run-time system-wide default policy => local allocation
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*/
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struct mempolicy default_policy = {
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.refcnt = ATOMIC_INIT(1), /* never free it */
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.mode = MPOL_DEFAULT,
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.mode = MPOL_PREFERRED,
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.v = { .preferred_node = -1 },
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};
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static const struct mempolicy_operations {
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@ -189,7 +193,7 @@ static struct mempolicy *mpol_new(unsigned short mode, unsigned short flags,
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if (mode == MPOL_DEFAULT) {
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if (nodes && !nodes_empty(*nodes))
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return ERR_PTR(-EINVAL);
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return NULL;
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return NULL; /* simply delete any existing policy */
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}
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VM_BUG_ON(!nodes);
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@ -246,7 +250,6 @@ void __mpol_put(struct mempolicy *p)
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{
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if (!atomic_dec_and_test(&p->refcnt))
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return;
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p->mode = MPOL_DEFAULT;
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kmem_cache_free(policy_cache, p);
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}
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@ -626,13 +629,16 @@ static long do_set_mempolicy(unsigned short mode, unsigned short flags,
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return 0;
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}
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/* Fill a zone bitmap for a policy */
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static void get_zonemask(struct mempolicy *p, nodemask_t *nodes)
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/*
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* Return nodemask for policy for get_mempolicy() query
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*/
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static void get_policy_nodemask(struct mempolicy *p, nodemask_t *nodes)
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{
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nodes_clear(*nodes);
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if (p == &default_policy)
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return;
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switch (p->mode) {
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case MPOL_DEFAULT:
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break;
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case MPOL_BIND:
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/* Fall through */
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case MPOL_INTERLEAVE:
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@ -686,6 +692,11 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
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}
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if (flags & MPOL_F_ADDR) {
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/*
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* Do NOT fall back to task policy if the
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* vma/shared policy at addr is NULL. We
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* want to return MPOL_DEFAULT in this case.
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*/
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down_read(&mm->mmap_sem);
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vma = find_vma_intersection(mm, addr, addr+1);
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if (!vma) {
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@ -700,7 +711,7 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
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return -EINVAL;
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if (!pol)
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pol = &default_policy;
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pol = &default_policy; /* indicates default behavior */
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if (flags & MPOL_F_NODE) {
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if (flags & MPOL_F_ADDR) {
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@ -715,8 +726,11 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
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err = -EINVAL;
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goto out;
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}
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} else
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*policy = pol->mode | pol->flags;
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} else {
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*policy = pol == &default_policy ? MPOL_DEFAULT :
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pol->mode;
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*policy |= pol->flags;
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}
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if (vma) {
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up_read(¤t->mm->mmap_sem);
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@ -725,7 +739,7 @@ static long do_get_mempolicy(int *policy, nodemask_t *nmask,
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err = 0;
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if (nmask)
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get_zonemask(pol, nmask);
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get_policy_nodemask(pol, nmask);
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out:
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mpol_cond_put(pol);
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@ -1286,8 +1300,7 @@ static struct mempolicy *get_vma_policy(struct task_struct *task,
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addr);
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if (vpol)
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pol = vpol;
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} else if (vma->vm_policy &&
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vma->vm_policy->mode != MPOL_DEFAULT)
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} else if (vma->vm_policy)
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pol = vma->vm_policy;
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}
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if (!pol)
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@ -1334,7 +1347,6 @@ static struct zonelist *policy_zonelist(gfp_t gfp, struct mempolicy *policy)
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nd = first_node(policy->v.nodes);
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break;
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case MPOL_INTERLEAVE: /* should not happen */
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case MPOL_DEFAULT:
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nd = numa_node_id();
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break;
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default:
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@ -1369,9 +1381,15 @@ static unsigned interleave_nodes(struct mempolicy *policy)
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*/
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unsigned slab_node(struct mempolicy *policy)
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{
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unsigned short pol = policy ? policy->mode : MPOL_DEFAULT;
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if (!policy)
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return numa_node_id();
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switch (policy->mode) {
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case MPOL_PREFERRED:
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if (unlikely(policy->v.preferred_node >= 0))
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return policy->v.preferred_node;
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return numa_node_id();
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switch (pol) {
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case MPOL_INTERLEAVE:
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return interleave_nodes(policy);
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@ -1390,13 +1408,8 @@ unsigned slab_node(struct mempolicy *policy)
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return zone->node;
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}
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case MPOL_PREFERRED:
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if (policy->v.preferred_node >= 0)
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return policy->v.preferred_node;
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/* Fall through */
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default:
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return numa_node_id();
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BUG();
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}
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}
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@ -1650,8 +1663,6 @@ int __mpol_equal(struct mempolicy *a, struct mempolicy *b)
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if (a->mode != MPOL_DEFAULT && !mpol_match_intent(a, b))
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return 0;
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switch (a->mode) {
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case MPOL_DEFAULT:
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return 1;
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case MPOL_BIND:
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/* Fall through */
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case MPOL_INTERLEAVE:
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@ -1828,7 +1839,7 @@ void mpol_shared_policy_init(struct shared_policy *info, unsigned short policy,
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if (policy != MPOL_DEFAULT) {
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struct mempolicy *newpol;
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/* Falls back to MPOL_DEFAULT on any error */
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/* Falls back to NULL policy [MPOL_DEFAULT] on any error */
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newpol = mpol_new(policy, flags, policy_nodes);
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if (!IS_ERR(newpol)) {
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/* Create pseudo-vma that contains just the policy */
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@ -1952,9 +1963,14 @@ static inline int mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
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char *p = buffer;
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int l;
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nodemask_t nodes;
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unsigned short mode = pol ? pol->mode : MPOL_DEFAULT;
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unsigned short mode;
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unsigned short flags = pol ? pol->flags : 0;
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if (!pol || pol == &default_policy)
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mode = MPOL_DEFAULT;
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else
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mode = pol->mode;
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switch (mode) {
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case MPOL_DEFAULT:
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nodes_clear(nodes);
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