diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/vm/numa_memory_policy.txt | 54 |
1 files changed, 18 insertions, 36 deletions
diff --git a/Documentation/vm/numa_memory_policy.txt b/Documentation/vm/numa_memory_policy.txt index 6719d642653f..13cca5a3cf17 100644 --- a/Documentation/vm/numa_memory_policy.txt +++ b/Documentation/vm/numa_memory_policy.txt @@ -147,35 +147,18 @@ 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. - - 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. + 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. + + When specified in one of the memory policy APIs, the Default mode + does not use the optional set of nodes. It is an error for the set of nodes specified for this policy to be non-empty. @@ -187,19 +170,18 @@ Components of Memory Policies 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 + 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. containing the cpu where the allocation takes place. 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. It is possible for the user to specify that local allocation is always preferred by passing an empty nodemask with this mode. |