+ mm-compactoin-fix-misbehaviors-of-fast_find_migrateblock.patch added to -mm tree

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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




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