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SubjectRe: [PATCH 1/1] doc, mempolicy: Fix wrong document in numa_memory_policy.txt
On 04/01/2014 08:53 PM, Tang Chen wrote:
> In document numa_memory_policy.txt, the following examples for flag
> MPOL_F_RELATIVE_NODES are incorrect.
>
> For example, consider a task that is attached to a cpuset with
> mems 2-5 that sets an Interleave policy over the same set with
> MPOL_F_RELATIVE_NODES. If the cpuset's mems change to 3-7, the
> interleave now occurs over nodes 3,5-6. If the cpuset's mems
> then change to 0,2-3,5, then the interleave occurs over nodes
> 0,3,5.
>
> According to the comment of the patch adding flag MPOL_F_RELATIVE_NODES,
> the nodemasks the user specifies should be considered relative to the
> current task's mems_allowed.
> (https://lkml.org/lkml/2008/2/29/428)
>
> And according to numa_memory_policy.txt, if the user's nodemask includes
> nodes that are outside the range of the new set of allowed nodes, then
> the remap wraps around to the beginning of the nodemask and, if not already
> set, sets the node in the mempolicy nodemask.
>
> So in the example, if the user specifies 2-5, for a task whose mems_allowed
> is 3-7, the nodemasks should be remapped the third, fourth, fifth, sixth
> node in mems_allowed. like the following:
>
> mems_allowed: 3 4 5 6 7
>
> relative index: 0 1 2 3 4
> 5
>
> So the nodemasks should be remapped to 3,5-7, but not 3,5-6.
>
> And for a task whose mems_allowed is 0,2-3,5, the nodemasks should be
> remapped to 0,2-3,5, but not 0,3,5.
>
> mems_allowed: 0 2 3 5
>
> relative index: 0 1 2 3
> 4 5
>
>
> Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>

Wow. This was not an April fools joke, right?

Have there been any acks of this? I haven't seen any responses to it.

Andrew, do you want to merge it?


> ---
> Documentation/vm/numa_memory_policy.txt | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/vm/numa_memory_policy.txt b/Documentation/vm/numa_memory_policy.txt
> index 4e7da65..badb050 100644
> --- a/Documentation/vm/numa_memory_policy.txt
> +++ b/Documentation/vm/numa_memory_policy.txt
> @@ -174,7 +174,6 @@ Components of Memory Policies
> 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. When the internal
> @@ -275,9 +274,9 @@ Components of Memory Policies
> For example, consider a task that is attached to a cpuset with
> mems 2-5 that sets an Interleave policy over the same set with
> MPOL_F_RELATIVE_NODES. If the cpuset's mems change to 3-7, the
> - interleave now occurs over nodes 3,5-6. If the cpuset's mems
> + interleave now occurs over nodes 3,5-7. If the cpuset's mems
> then change to 0,2-3,5, then the interleave occurs over nodes
> - 0,3,5.
> + 0,2-3,5.
>
> Thanks to the consistent remapping, applications preparing
> nodemasks to specify memory policies using this flag should
>


--
~Randy


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