Since current_order starts as MAX_ORDER-1 and is then only decremented, the second half of the loop condition seems superfluous. However, if order is 0, we may decrement current_order past 0, making it UINT_MAX. This is obviously too subtle ([1], [2]).
Since we need to add some comment anyway, change the two variables to signed, making the counting-down for loop look more familiar, and apparently also making gcc generate slightly smaller code. [1] https://lkml.org/lkml/2016/6/20/493 [2] https://lkml.org/lkml/2017/6/19/345 Signed-off-by: Rasmus Villemoes <[email protected]> --- Michal, something like this, perhaps? mm/page_alloc.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 2302f250d6b1..e656f4da9772 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2204,19 +2204,23 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac, * list of requested migratetype, possibly along with other pages from the same * block, depending on fragmentation avoidance heuristics. Returns true if * fallback was found so that __rmqueue_smallest() can grab it. + * + * The use of signed ints for order and current_order is a deliberate + * deviation from the rest of this file, to make the for loop + * condition simpler. */ static inline bool -__rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype) +__rmqueue_fallback(struct zone *zone, int order, int start_migratetype) { struct free_area *area; - unsigned int current_order; + int current_order; struct page *page; int fallback_mt; 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 >= order; --current_order) { area = &(zone->free_area[current_order]); fallback_mt = find_suitable_fallback(area, current_order, -- 2.11.0
