In the fast_find_migrateblock(), It iterate freelist to find
proper pageblock. But there are some misbehaviors.
First, if the page we found is equal to cc->migrate_pfn, it
is considered that we didn't found suitable pageblock. Second,
if the loop was terminated because order is less than
PAGE_ALLOC_COSTLY_ORDER, it could be considered that we found
suitable one. Third, if the skip bit is set on the page block
and go continue, it doesn't check the nr_scanned. Fourth, if
the page block's skip bit is set, it check that page block is
the last of list. But it is unnecessary.
Fixes: 70b44595eafe9 ("mm, compaction: use free lists to quickly locate
a migration source")
Signed-off-by: Wonhyuk Yang <vvghjk1234@xxxxxxxxx>
---
Changes in v2:
- Follow Vlastimil's suggestions, using bool varable.
- Fix new misbehavior and remove unecessary .
v1: https://lore.kernel.org/linux-mm/20210123154320.24278-1-vvghjk1234@xxxxxxxxx
---
mm/compaction.c | 27 ++++++++++++---------------
1 file changed, 12 insertions(+), 15 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index e5acb9714436..8e5cd9d20435 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1701,6 +1701,7 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
unsigned long pfn = cc->migrate_pfn;
unsigned long high_pfn;
int order;
+ bool found_block = false;
/* Skip hints are relied on to avoid repeats on the fast search */
if (cc->ignore_skip_hint)
@@ -1743,7 +1744,7 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
high_pfn = pageblock_start_pfn(cc->migrate_pfn + distance);
for (order = cc->order - 1;
- order >= PAGE_ALLOC_COSTLY_ORDER && pfn == cc->migrate_pfn && nr_scanned < limit;
+ order >= PAGE_ALLOC_COSTLY_ORDER && !found_block && nr_scanned < limit;
order--) {
struct free_area *area = &cc->zone->free_area[order];
struct list_head *freelist;
@@ -1758,7 +1759,11 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
list_for_each_entry(freepage, freelist, lru) {
unsigned long free_pfn;
- nr_scanned++;
+ if (nr_scanned++ >= limit) {
+ move_freelist_tail(freelist, freepage);
+ break;
+ }
+
free_pfn = page_to_pfn(freepage);
if (free_pfn < high_pfn) {
/*
@@ -1767,12 +1772,8 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
* the list assumes an entry is deleted, not
* reordered.
*/
- if (get_pageblock_skip(freepage)) {
- if (list_is_last(freelist, &freepage->lru))
- break;
-
+ if (get_pageblock_skip(freepage))
continue;
- }
/* Reorder to so a future search skips recent pages */
move_freelist_tail(freelist, freepage);
@@ -1780,15 +1781,10 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
update_fast_start_pfn(cc, free_pfn);
pfn = pageblock_start_pfn(free_pfn);
cc->fast_search_fail = 0;
+ found_block = true;
set_pageblock_skip(freepage);
break;
}
-
- if (nr_scanned >= limit) {
- cc->fast_search_fail++;
- move_freelist_tail(freelist, freepage);
- break;
- }
}
spin_unlock_irqrestore(&cc->zone->lock, flags);
}
@@ -1799,9 +1795,10 @@ static unsigned long fast_find_migrateblock(struct compact_control *cc)
* If fast scanning failed then use a cached entry for a page block
* that had free pages as the basis for starting a linear scan.
*/
- if (pfn == cc->migrate_pfn)
+ if (!found_block) {
+ cc->fast_search_fail++;
pfn = reinit_migrate_pfn(cc);
-
+ }
return pfn;
}
--
2.25.1
