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SubjectRe: [PATCH 1/2] mm: change free_cma and free_pages declarations to unsigned
On Tue, Sep 29, 2015 at 11:13:27AM +0100, Mel Gorman wrote:
> On Sun, Sep 27, 2015 at 09:04:16PM +0000, Alexandru Moise wrote:
> > Their stored values come from zone_page_state() which returns
> > an unsigned long. To improve code correctness we should avoid
> > mixing signed and unsigned integers.
> >
> > Signed-off-by: Alexandru Moise <00moses.alexander00@gmail.com>
> > ---
> > mm/page_alloc.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 48aaf7b..f55e3a2 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -2242,7 +2242,7 @@ static bool __zone_watermark_ok(struct zone *z, unsigned int order,
> > /* free_pages may go negative - that's OK */
> > long min = mark;
> > int o;
> > - long free_cma = 0;
> > + unsigned long free_cma = 0;
> >
>
> NAK.
>
> free_cma is used with free_pages which is explicitly commented as saying
> it can go negative. With your patch, there is a signed/unsigned operation
> where the unsigned type cannot fit into the signed type which casts them
> both to unsigned which is then broken for the comparison. This patch
> looks broken for very subtle reasons. Please do not do any similar style
> patches to this because they can introduce subtle breakage if issues are
> not caught at review.
>

Understood, I thought the comment only applied to the "min" variable.


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