This is a note to let you know that I've just added the patch titled
mm/compaction: fix misbehaviors of fast_find_migrateblock()
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-compaction-fix-misbehaviors-of-fast_find_migrateb.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit ed6a70cb697f9d91ac269cf64fe034363251ff9f
Author: Wonhyuk Yang <vvghjk1234@xxxxxxxxx>
Date: Wed Feb 24 12:09:36 2021 -0800
mm/compaction: fix misbehaviors of fast_find_migrateblock()
[ Upstream commit 15d28d0d11609c7a4f217b3d85e26456d9beb134 ]
In the fast_find_migrateblock(), it iterates ocer the freelist to find the
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 find a suitable pageblock. Secondly, if the loop was
terminated because order is less than PAGE_ALLOC_COSTLY_ORDER, it could be
considered that we found a suitable one. Thirdly, if the skip bit is set
on the page block and we goto continue, it doesn't check nr_scanned.
Fourthly, if the page block's skip bit is set, it checks that page block
is the last of list, which is unnecessary.
Link: https://lkml.kernel.org/r/20210128130411.6125-1-vvghjk1234@xxxxxxxxx
Fixes: 70b44595eafe9 ("mm, compaction: use free lists to quickly locate a migration source")
Signed-off-by: Wonhyuk Yang <vvghjk1234@xxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/mm/compaction.c b/mm/compaction.c
index 0846d4ffa3387..21dcae9d7df3c 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1662,6 +1662,7 @@ 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)
@@ -1704,7 +1705,7 @@ 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;
@@ -1719,7 +1720,11 @@ 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) {
/*
@@ -1728,12 +1733,8 @@ 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);
@@ -1741,15 +1742,10 @@ 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);
}
@@ -1760,9 +1756,10 @@ 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;
}
