Compaction migration scanner marks a pageblock as unsuitable (via pageblock
skip bit) if it fails to isolate any pages in them. When scanning for async
direct compaction, it skips all pages of a order-aligned block once a page
fails isolation, because a single page is enough to prevent forming a free page
of given order. But the skipped pages might still be migratable and form a free
page of a lower order. Therefore we should not mark pageblock unsuitable, if
skipping has happened. The worst example would be a THP allocation attempt
marking pageblock unsuitable due to a single page, so the following lower-order
and more critical allocation will skip the pageblock.
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
mm/compaction.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index b8c23882c8ae..ce73badad464 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -698,7 +698,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
bool locked = false;
struct page *page = NULL, *valid_page = NULL;
unsigned long start_pfn = low_pfn;
- bool skip_on_failure = false;
+ bool skip_on_failure = false, skipped_pages = false;
unsigned long next_skip_pfn = 0;
/*
@@ -920,13 +920,14 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
nr_isolated = 0;
}
- if (low_pfn < next_skip_pfn) {
+ if (low_pfn < next_skip_pfn - 1) {
low_pfn = next_skip_pfn - 1;
/*
* The check near the loop beginning would have updated
* next_skip_pfn too, but this is a bit simpler.
*/
next_skip_pfn += 1UL << cc->order;
+ skipped_pages = true;
}
}
@@ -944,7 +945,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
* Update the pageblock-skip information and cached scanner pfn,
* if the whole pageblock was scanned without isolating any page.
*/
- if (low_pfn == end_pfn)
+ if (low_pfn == end_pfn && !skipped_pages)
update_pageblock_skip(cc, valid_page, nr_isolated, true);
trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
--
2.15.1
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