On 11/29/2023 6:45 PM, Barry Song wrote:
Testing shows fast_isolate_freepages can blindly choose an unsuitable
pageblock from time to time particularly while the min mark is used
from XXX path:
if (!page) {
cc->fast_search_fail++;
if (scan_start) {
/*
* Use the highest PFN found above min. If one was
* not found, be pessimistic for direct compaction
* and use the min mark.
*/
if (highest >= min_pfn) {
page = pfn_to_page(highest);
cc->free_pfn = highest;
} else {
if (cc->direct_compaction && pfn_valid(min_pfn)) { /* XXX */
page = pageblock_pfn_to_page(min_pfn,
min(pageblock_end_pfn(min_pfn),
zone_end_pfn(cc->zone)),
cc->zone);
cc->free_pfn = min_pfn;
}
}
}
}
Yes, the min_pfn can be an unsuitable migration target. But I think we
can just add the suitable_migration_target() validation into 'min_pfn'
case? Since other cases must be suitable target which found from
MIGRATE_MOVABLE free list. Something like below:
diff --git a/mm/compaction.c b/mm/compaction.c
index 01ba298739dd..4e8eb4571909 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1611,6 +1611,8 @@ static void fast_isolate_freepages(struct
compact_control *cc)
min(pageblock_end_pfn(min_pfn),
zone_end_pfn(cc->zone)),
cc->zone);
+ if
(!suitable_migration_target(cc, page))
+ page = NULL;
cc->free_pfn = min_pfn;
}
}
By the way, I wonder if this patch can improve the efficiency of
compaction in your test case?
In contrast, slow path is skipping unsuitable pageblocks in a decent way.
I don't know if it is an intended design or just an oversight. But
it seems more sensible to skip unsuitable pageblock.
Reported-by: Zhanyuan Hu <huzhanyuan@xxxxxxxx>
Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
---
mm/compaction.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/mm/compaction.c b/mm/compaction.c
index 01ba298739dd..98c485a25614 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1625,6 +1625,12 @@ static void fast_isolate_freepages(struct compact_control *cc)
cc->total_free_scanned += nr_scanned;
if (!page)
return;
+ /*
+ * Otherwise, we can blindly choose an improper pageblock especially
+ * while using the min mark
+ */
+ if (!suitable_migration_target(cc, page))
+ return;
low_pfn = page_to_pfn(page);
fast_isolate_around(cc, low_pfn);
