Messages in this thread | | | From | Rasmus Villemoes <> | Subject | Re: [PATCH] mm: remove a redundant condition in the for loop | Date | Mon, 19 Jun 2017 21:05:29 +0200 |
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On Mon, Jun 19 2017, Vlastimil Babka <vbabka@suse.cz> wrote:
> On 06/19/2017 03:54 PM, Hao Lee wrote: >> The variable current_order decreases from MAX_ORDER-1 to order, so the >> condition current_order <= MAX_ORDER-1 is always true. >> >> Signed-off-by: Hao Lee <haolee.swjtu@gmail.com> > > Sounds right. > > Acked-by: Vlastimil Babka <vbabka@suse.cz>
current_order and order are both unsigned, and if order==0, current_order >= order is always true, and we may decrement current_order past 0 making it UINT_MAX... A comment would be in order, though.
>> --- >> mm/page_alloc.c | 5 ++--- >> 1 file changed, 2 insertions(+), 3 deletions(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 2302f25..9120c2b 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -2215,9 +2215,8 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype) >> bool can_steal; >> >> /* Find the largest possible block of pages in the other list */ >> - for (current_order = MAX_ORDER-1; >> - current_order >= order && current_order <= MAX_ORDER-1; >> - --current_order) { >> + for (current_order = MAX_ORDER-1; current_order >= order; >> + --current_order) { >> area = &(zone->free_area[current_order]); >> fallback_mt = find_suitable_fallback(area, current_order, >> start_migratetype, false, &can_steal); >>
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