From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lee Schermerhorn Date: Thu, 06 Dec 2007 16:21:23 -0500 Message-Id: <20071206212123.6279.22285.sendpatchset@localhost> In-Reply-To: <20071206212047.6279.10881.sendpatchset@localhost> References: <20071206212047.6279.10881.sendpatchset@localhost> Subject: [PATCH/RFC 6/8] Mem Policy: Use MPOL_PREFERRED for system-wide default policy Sender: owner-linux-mm@kvack.org Return-Path: To: linux-mm@kvack.org Cc: akpm@linux-foundation.org, clameter@sgi.com, ak@suse.de, eric.whitney@hp.com, mel@skynet.ie List-ID: PATCH/RFC 06/08 Mem Policy: Use MPOL_PREFERRED for system-wide default policy Against: 2.6.24-rc2-mm1 V2 -> V3: + mpol_to_str(): show "default" policy when &default_policy is passed in, rather than the details of the default_policy, in /proc//numa_maps. V1 -> V2: + restore BUG()s in switch(policy) default cases -- per Christoph + eliminate unneeded re-init of struct mempolicy policy member before freeing 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. This patch updates Documentation to reflect this change. Tested with set_mempolicy() using numactl with memtoy, and tested mbind() with memtoy. All seems to work "as expected". Signed-off-by: Lee Schermerhorn Documentation/vm/numa_memory_policy.txt | 70 ++++++++++++-------------------- mm/mempolicy.c | 38 +++++++++-------- 2 files changed, 47 insertions(+), 61 deletions(-) Index: Linux/mm/mempolicy.c =================================================================== --- Linux.orig/mm/mempolicy.c 2007-12-06 14:18:34.000000000 -0500 +++ Linux/mm/mempolicy.c 2007-12-06 14:20:17.000000000 -0500 @@ -105,9 +105,13 @@ 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 struct mempolicy *get_vma_policy(struct task_struct *task, @@ -166,7 +170,8 @@ static struct mempolicy *mpol_new(int mo mode, nodes ? nodes_addr(*nodes)[0] : -1); if (mode == MPOL_DEFAULT) - return NULL; + return NULL; /* simply delete any existing policy */ + policy = kmem_cache_alloc(policy_cache, GFP_KERNEL); if (!policy) return ERR_PTR(-ENOMEM); @@ -484,8 +489,6 @@ static void get_zonemask(struct mempolic { nodes_clear(*nodes); switch (policy_mode(p)) { - case MPOL_DEFAULT: - break; case MPOL_BIND: /* Fall through */ case MPOL_INTERLEAVE: @@ -1130,8 +1133,7 @@ static struct mempolicy *get_vma_policy( addr); if (vpol) pol = vpol; - } else if (vma->vm_policy && - policy_mode(vma->vm_policy) != MPOL_DEFAULT) + } else if (vma->vm_policy) pol = vma->vm_policy; } if (!pol) @@ -1175,7 +1177,6 @@ static struct zonelist *zonelist_policy( nd = first_node(policy->v.nodes); break; case MPOL_INTERLEAVE: /* should not happen */ - case MPOL_DEFAULT: nd = numa_node_id(); break; default: @@ -1209,9 +1210,10 @@ static unsigned interleave_nodes(struct */ unsigned slab_node(struct mempolicy *policy) { - int pol = policy ? policy_mode(policy) : MPOL_DEFAULT; + if (!policy) + return numa_node_id(); - switch (pol) { + switch (policy_mode(policy)) { case MPOL_INTERLEAVE: return interleave_nodes(policy); @@ -1232,10 +1234,10 @@ unsigned slab_node(struct mempolicy *pol case MPOL_PREFERRED: if (policy->v.preferred_node >= 0) return policy->v.preferred_node; - /* Fall through */ + return numa_node_id(); default: - return numa_node_id(); + BUG(); } } @@ -1450,8 +1452,6 @@ int __mpol_equal(struct mempolicy *a, st return 0; switch (policy_mode(a)) { - case MPOL_DEFAULT: - return 1; case MPOL_BIND: /* Fall through */ case MPOL_INTERLEAVE: @@ -1469,7 +1469,6 @@ void __mpol_free(struct mempolicy *p) { if (!atomic_dec_and_test(&p->refcnt)) return; - p->mode = MPOL_DEFAULT; kmem_cache_free(policy_cache, p); } @@ -1637,7 +1636,7 @@ void mpol_shared_policy_init(struct shar 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, policy_nodes); if (!IS_ERR(newpol)) { /* Create pseudo-vma that contains just the policy */ @@ -1758,8 +1757,6 @@ static void mpol_rebind_policy(struct me return; switch (policy_mode(pol)) { - case MPOL_DEFAULT: - break; case MPOL_BIND: /* Fall through */ case MPOL_INTERLEAVE: @@ -1823,7 +1820,12 @@ static inline int mpol_to_str(char *buff char *p = buffer; int l; nodemask_t nodes; - int mode = pol ? policy_mode(pol) : MPOL_DEFAULT; + int mode; + + if (!pol || pol == &default_policy) + mode = MPOL_DEFAULT; + else + mode = policy_mode(pol); switch (mode) { case MPOL_DEFAULT: Index: Linux/Documentation/vm/numa_memory_policy.txt =================================================================== --- Linux.orig/Documentation/vm/numa_memory_policy.txt 2007-12-06 14:18:34.000000000 -0500 +++ Linux/Documentation/vm/numa_memory_policy.txt 2007-12-06 14:18:39.000000000 -0500 @@ -145,63 +145,47 @@ Components of Memory Policies Linux memory policy supports the following 4 behavioral modes: - Default Mode--MPOL_DEFAULT: The behavior specified by this mode is - context or scope dependent. + Default Mode--MPOL_DEFAULT: This mode is only used in the memory + policy APIs. Internally, MPOL_DEFAULT is converted to the NULL + memory policy in all policy scopes. Any existing non-default policy + will simply be removed when MPOL_DEFAULT is specified. As a result, + MPOL_DEFAULT means "fall back to the next most specific policy scope." + + For example, a NULL or default task policy will fall back to the + system default policy. A NULL or default vma policy will fall + back to the task policy. - As mentioned in the Policy Scope section above, during normal - system operation, the System Default Policy is hard coded to - contain the Default mode. - - In this context, default mode means "local" allocation--that is - attempt to allocate the page from the node associated with the cpu - where the fault occurs. If the "local" node has no memory, or the - node's memory can be exhausted [no free pages available], local - allocation will "fallback to"--attempt to allocate pages from-- - "nearby" nodes, in order of increasing "distance". - - Implementation detail -- subject to change: "Fallback" uses - a per node list of sibling nodes--called zonelists--built at - boot time, or when nodes or memory are added or removed from - the system [memory hotplug]. These per node zonelist are - constructed with nodes in order of increasing distance based - on information provided by the platform firmware. - - When a task/process policy or a shared policy contains the Default - mode, this also means "local allocation", as described above. - - In the context of a VMA, Default mode means "fall back to task - policy"--which may or may not specify Default mode. Thus, Default - mode can not be counted on to mean local allocation when used - on a non-shared region of the address space. However, see - MPOL_PREFERRED below. - - The Default mode does not use the optional set of nodes. + When specified in one of the memory policy APIs, the Default mode + does not use the optional set of nodes. MPOL_BIND: This mode specifies that memory must come from the set of nodes specified by the policy. The memory policy APIs do not specify an order in which the nodes - will be searched. However, unlike "local allocation", the Bind - policy does not consider the distance between the nodes. Rather, - allocations will fallback to the nodes specified by the policy in - order of numeric node id. Like everything in Linux, this is subject - to change. + will be searched. However, unlike "local allocation" discussed + below, the Bind policy does not consider the distance between the + nodes. Rather, allocations will fallback to the nodes specified + by the policy in order of numeric node id. Like everything in + Linux, this is subject to change. MPOL_PREFERRED: This mode specifies that the allocation should be attempted from the single node specified in the policy. If that - allocation fails, the kernel will search other nodes, exactly as - it would for a local allocation that started at the preferred node - in increasing distance from the preferred node. "Local" allocation - policy can be viewed as a Preferred policy that starts at the node - containing the cpu where the allocation takes place. + allocation fails, the kernel will search other nodes, in order of + increasing distance from the preferred node based on information + provided by the platform firmware. Internally, the Preferred policy uses a single node--the preferred_node member of struct mempolicy. A "distinguished value of this preferred_node, currently '-1', is interpreted as "the node containing the cpu where the allocation takes - place"--local allocation. This is the way to specify - local allocation for a specific range of addresses--i.e. for - VMA policies. + place"--local allocation. "Local" allocation policy can be + viewed as a Preferred policy that starts at the node containing + the cpu where the allocation takes place. + + As mentioned in the Policy Scope section above, during normal + system operation, the System Default Policy is hard coded to + specify "local allocation". This policy uses the Preferred + policy with the special negative value of preferred_node. MPOL_INTERLEAVED: This mode specifies that page allocations be interleaved, on a page granularity, across the nodes specified in -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org