The patch titled
Subject: mm/compaction: fix misbehaviors of fast_find_migrateblock()
has been added to the -mm tree. Its filename is
mm-compactoin-fix-misbehaviors-of-fast_find_migrateblock.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-compactoin-fix-misbehaviors-of-fast_find_migrateblock.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-compactoin-fix-misbehaviors-of-fast_find_migrateblock.patch
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------------------------------------------------------
From: Wonhyuk Yang <vvghjk1234@xxxxxxxxx>
Subject: mm/compaction: fix misbehaviors of fast_find_migrateblock()
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.
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>
---
mm/compaction.c | 27 ++++++++++++---------------
1 file changed, 12 insertions(+), 15 deletions(-)
--- a/mm/compaction.c~mm-compactoin-fix-misbehaviors-of-fast_find_migrateblock
+++ a/mm/compaction.c
@@ -1698,6 +1698,7 @@ static unsigned long fast_find_migratebl
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)
@@ -1740,7 +1741,7 @@ static unsigned long fast_find_migratebl
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;
@@ -1755,7 +1756,11 @@ static unsigned long fast_find_migratebl
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) {
/*
@@ -1764,12 +1769,8 @@ static unsigned long fast_find_migratebl
* 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);
@@ -1777,15 +1778,10 @@ static unsigned long fast_find_migratebl
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);
}
@@ -1796,9 +1792,10 @@ static unsigned long fast_find_migratebl
* 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;
}
_
Patches currently in -mm which might be from vvghjk1234@xxxxxxxxx are
mm-compactoin-fix-misbehaviors-of-fast_find_migrateblock.patch
