Re: [PATCH 1/1] doc, mempolicy: Fix wrong document in numa_memory_policy.txt

[Tang Chen]

Hi Randy,

On 04/11/2014 07:23 AM, Randy Dunlap wrote:
> 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@xxxxxxxxxxxxxx>
>
> Wow.  This was not an April fools joke, right?
>
> Have there been any acks of this?  I haven't seen any responses to it.

Thanks for the reply. I found this problem when I was reading the doc.
I think it is wrong. And according to the original patch:

https://lkml.org/lkml/2008/2/29/428

I think it should be fixed in the above way. But if I was wrong, please
let me know, and I think we can at least improve the doc since it is
not that easy to understand.

Thanks. :)

> 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
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