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SubjectRe: [bug ?] do_get_mempolicy()
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On Thu, 2008-07-03 at 16:44 -0400, John Blackwood wrote:
> Hi Lee,

John: I'm just getting back from a long weekend and I'm wading through
a big e-mail back log. I'll take a look at this when I get to the end
of my inbox. I/m probably responsible for that line. I recall thinking
that get_mempolicy() should return the policy that one would pass back
in to achieve the same effect. But, I blew it.

>
> I'm having unexpected results with get_mempolicy(2) in 2.6.26, and
> I am hoping that you can either agree with me, or maybe comment on my
> misconceptions.
>
> When I have a task with no special task mempolicy (the default mempolicy),
> when I call get_mempolicy(2), it returns a policy value of 2 (MPOL_BIND)
> with a NULL nodemask.
>
> I believe that this is because of the code in do_get_mempolicy() that does:
>
> *policy |= pol->flags;
>
> in the else case when flags do not contain MPOL_F_NODE.

I think that need to mask off the internal flags, and shift the
remaining ones up to the correct location. I'll send a patch, if no one
beats me to it.

>
> I guess I don't understand why we are ORing in the pol->flags into the
> *policy value. For example, when this is for the default_policy, the
> MPOL_F_LOCAL flag (which has a value of 2) gets stuffed into the *policy
> location, and a get_mempolicy(2) caller sees this as the MPOL_BIND
> mempolicy.
>
> Maybe the "*policy |= pol->flags;" line should be removed ?
>
> That is, maybe it was valid at some point, but subsequent changes
> make this line of code no longer valid ?
>
> Sorry if I'm out-to-lunch here...

No, doesn't appear that way..

>
> Thanks very much for you time and considerations on this issue.
>

thanks for reporting it.

Lee



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