The patch titled
Subject: mm/page_alloc.c: eliminate unsigned confusion in __rmqueue_fallback
has been added to the -mm tree. Its filename is
mm-page_allocc-eliminate-unsigned-confusion-in-__rmqueue_fallback.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-page_allocc-eliminate-unsigned-confusion-in-__rmqueue_fallback.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-page_allocc-eliminate-unsigned-confusion-in-__rmqueue_fallback.patch
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From: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Subject: mm/page_alloc.c: eliminate unsigned confusion in __rmqueue_fallback
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
Link: http://lkml.kernel.org/r/20170621185529.2265-1-linux@xxxxxxxxxxxxxxxxxx
Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff -puN mm/page_alloc.c~mm-page_allocc-eliminate-unsigned-confusion-in-__rmqueue_fallback mm/page_alloc.c
--- a/mm/page_alloc.c~mm-page_allocc-eliminate-unsigned-confusion-in-__rmqueue_fallback
+++ a/mm/page_alloc.c
@@ -2206,12 +2206,16 @@ static bool unreserve_highatomic_pageblo
* 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)
{
struct free_area *area;
- unsigned int current_order;
+ int current_order;
struct page *page;
int fallback_mt;
bool can_steal;
@@ -2221,8 +2225,7 @@ __rmqueue_fallback(struct zone *zone, un
* approximates finding the pageblock with the most free pages, which
* would be too costly to do exactly.
*/
- for (current_order = MAX_ORDER-1;
- current_order >= order && current_order <= MAX_ORDER-1;
+ 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,
_
Patches currently in -mm which might be from linux@xxxxxxxxxxxxxxxxxx are
mm-page_allocc-eliminate-unsigned-confusion-in-__rmqueue_fallback.patch
kernel-groupsc-use-sort-library-function.patch
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