[patch] mm, page_alloc: set num_movable in move_freepages()

[patch] mm, page_alloc: set num_movable in move_freepages()

[David Rientjes]

If move_freepages() returns 0 because zone_spans_pfn(), *num_movable can
hold the value from the stack because it does not get initialized in
move_freepages().

Move the initialization to move_freepages_block() to guarantee the value
actually makes sense.

This currently doesn't affect its only caller where num_movable != NULL,
so no bug fix, but just more robust.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/page_alloc.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2015,10 +2015,6 @@ static int move_freepages(struct zone *zone,
 	          pfn_valid(page_to_pfn(end_page)) &&
 	          page_zone(start_page) != page_zone(end_page));
 #endif
-
-	if (num_movable)
-		*num_movable = 0;
-
 	for (page = start_page; page <= end_page;) {
 		if (!pfn_valid_within(page_to_pfn(page))) {
 			page++;
@@ -2058,6 +2054,9 @@ int move_freepages_block(struct zone *zone, struct page *page,
 	unsigned long start_pfn, end_pfn;
 	struct page *start_page, *end_page;
 
+	if (num_movable)
+		*num_movable = 0;
+
 	start_pfn = page_to_pfn(page);
 	start_pfn = start_pfn & ~(pageblock_nr_pages-1);
 	start_page = pfn_to_page(start_pfn);

Re: [patch] mm, page_alloc: set num_movable in move_freepages()

[Andrew Morton]

On Fri, 5 Oct 2018 13:56:39 -0700 (PDT) David Rientjes <rientjes@google.com> wrote:

> If move_freepages() returns 0 because zone_spans_pfn(), *num_movable can

     move_free_pages_block()?           !zone_spans_pfn()?

> hold the value from the stack because it does not get initialized in
> move_freepages().
> 
> Move the initialization to move_freepages_block() to guarantee the value
> actually makes sense.
> 
> This currently doesn't affect its only caller where num_movable != NULL,
> so no bug fix, but just more robust.
> 
> ...

Re: [patch] mm, page_alloc: set num_movable in move_freepages()

[David Rientjes]

On Fri, 5 Oct 2018, Andrew Morton wrote:

> On Fri, 5 Oct 2018 13:56:39 -0700 (PDT) David Rientjes <rientjes@google.com> wrote:
> 
> > If move_freepages() returns 0 because zone_spans_pfn(), *num_movable can
> 
>      move_free_pages_block()?           !zone_spans_pfn()?
> 

move_freepages_block() more accurately, yes.  And yes, it depends on the 
return value of zone_spans_pfn().

Re: [patch] mm, page_alloc: set num_movable in move_freepages()

[Vlastimil Babka]

On 10/5/18 11:21 PM, Andrew Morton wrote:
> On Fri, 5 Oct 2018 13:56:39 -0700 (PDT) David Rientjes <rientjes@google.com> wrote:
> 
>> If move_freepages() returns 0 because zone_spans_pfn(), *num_movable can
> 
>      move_free_pages_block()?           !zone_spans_pfn()?

Also the subject would be more accurate if it said "initialize
num_movable in move_freepages_block()" ?

Otherwise,
Acked-by: Vlastimil Babka <vbabka@suse.cz>

>> hold the value from the stack because it does not get initialized in
>> move_freepages().
>>
>> Move the initialization to move_freepages_block() to guarantee the value
>> actually makes sense.
>>
>> This currently doesn't affect its only caller where num_movable != NULL,
>> so no bug fix, but just more robust.
>>
>> ...
>