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SubjectRe: [patch 1/4] mempolicy: convert MPOL constants to enum
On Mon, 11 Feb 2008, Christoph Lameter wrote:

> > The policy member of struct mempolicy is also converted from type short
> > to type unsigned short. A negative policy does not have any legitimate
> > meaning, so it is possible to change its type in preparation for adding
> > optional mode flags later.
> The second paragraphs seems to indicate that such an approach does not
> work since we also use MPOL_xx constants to set flags in the memory
> policies?

Not sure I'm understanding your question, sorry.

Mempolicy modes have always been int constants because it doesn't make
sense to combine them. Putting them into 'enum mempolicy_mode' leaves
that unchanged.

Mempolicy flags can be combined (even though my patchset only currently
implements one, it's easy to implement others). So they definitely cannot
be enum constants.

Regardless, storing the policy (mode | flags) in struct mempolicy as a
'short' doesn't help since a negative policy doesn't mean anything. In
preparation for allowing the upper MPOL_FLAG_SHIFT bits to be used to
store the flags of this member, I converted it to 'unsigned short'. This
is because the API with userspace is through 'int', which is implicitly
signed, and we don't want to sign-extend the upper bit if it's ever used
to hold a mempolicy flag.


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