mm: compaction: skip more fully scanned pageblock

In fast_isolate_around(), it assumes the pageblock is fully scanned if
cc->nr_freepages < cc->nr_migratepages after trying to isolate some free
pages, and will set skip flag to avoid scanning in future.  However this
can miss setting the skip flag for a fully scanned pageblock (returned
'start_pfn' is equal to 'end_pfn') in the case where cc->nr_freepages is
larger than cc->nr_migratepages.

So using the returned 'start_pfn' from isolate_freepages_block() and
'end_pfn' to decide if a pageblock is fully scanned makes more sense.  It
can also cover the case where cc->nr_freepages < cc->nr_migratepages,
which means the 'start_pfn' is usually equal to 'end_pfn' except some
uncommon fatal error occurs after non-strict mode isolation.

Link: https://lkml.kernel.org/r/f4efd2fa08735794a6d809da3249b6715ba6ad38.1685018752.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/compaction.c b/mm/compaction.c
index d4cee5803214cb74b52147ae5afcb289ca798ca6..c5f97bfd629c848badb0b8e04a33897140b2558f 100644 (file)
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1389,7 +1389,7 @@ fast_isolate_around(struct compact_control *cc, unsigned long pfn)
        isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false);
 
        /* Skip this pageblock in the future as it's full or nearly full */
-       if (cc->nr_freepages < cc->nr_migratepages)
+       if (start_pfn == end_pfn)
                set_pageblock_skip(page);
 
        return;