On Wed 21-06-17 20:55:28, Rasmus Villemoes wrote: > 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 <linux@xxxxxxxxxxxxxxxxxx> I would hope for a more consistent usage of the type but his alone should prevent future attempts to "clean up" the code. Acked-by: Michal Hocko <mhocko@xxxxxxxx> > --- > 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 > -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
