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SubjectRe: [Patch v2 2/2] mm/page_alloc.c: define node_order with all zero
On 03/28/20 at 12:26am, Wei Yang wrote:
> On Fri, Mar 27, 2020 at 03:37:57PM -0700, John Hubbard wrote:
> >On 3/27/20 3:01 PM, Wei Yang wrote:
> >> Since we always clear node_order before getting it, we can leverage
> >> compiler to do this instead of at run time.
> >>
> >> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> >> ---
> >> mm/page_alloc.c | 3 +--
> >> 1 file changed, 1 insertion(+), 2 deletions(-)
> >>
> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> >> index dfcf2682ed40..49dd1f25c000 100644
> >> --- a/mm/page_alloc.c
> >> +++ b/mm/page_alloc.c
> >> @@ -5585,7 +5585,7 @@ static void build_thisnode_zonelists(pg_data_t *pgdat)
> >> static void build_zonelists(pg_data_t *pgdat)
> >> {
> >> - static int node_order[MAX_NUMNODES];
> >> + static int node_order[MAX_NUMNODES] = {0};
> >
> >
> >Looks wrong: now the single instance of node_order is initialized just once by
> >the compiler. And that means that only the first caller of this function
> >gets a zeroed node_order array...
> >
>
> What a shame on me. You are right, I miss the static word.
>
> Well, then I am curious about why we want to define it as static. Each time we
> call this function, node_order would be set to 0 and find_next_best_node()
> would sort a proper value into it. I don't see the reason to reserve it in a
> global area and be used next time.
>
> My suggestion is to remove the static and define it {0} instead of memset
> every time. Is my understanding correct here?

Removing static looks good, the node_order is calculated on the basis of
each node, it's useless for other node. It may be inherited from the old
code where it's a static global variable.

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