Currently we will use 'cc->nr_freepages >= cc->nr_migratepages' comparison
to ensure that enough freepages are isolated in isolate_freepages(), however
it just decreases the cc->nr_freepages without updating cc->nr_migratepages
in compaction_alloc(), which will waste more CPU cycles and cause too many
freepages to be isolated.
So we should also update the cc->nr_migratepages when allocating or freeing
the freepages to avoid isolating excess freepages. And I can see fewer free
pages are scanned and isolated when running thpcompact on my Arm64 server:
k6.7 k6.7_patched
Ops Compaction pages isolated 120692036.00 118160797.00
Ops Compaction migrate scanned 131210329.00 154093268.00
Ops Compaction free scanned 1090587971.00 1080632536.00
Ops Compact scan efficiency 12.03 14.26
Moreover, I did not see an obvious latency improvements, this is likely because
isolating freepages is not the bottleneck in the thpcompact test case.
k6.7 k6.7_patched
Amean fault-both-1 1089.76 ( 0.00%) 1080.16 * 0.88%*
Amean fault-both-3 1616.48 ( 0.00%) 1636.65 * -1.25%*
Amean fault-both-5 2266.66 ( 0.00%) 2219.20 * 2.09%*
Amean fault-both-7 2909.84 ( 0.00%) 2801.90 * 3.71%*
Amean fault-both-12 4861.26 ( 0.00%) 4733.25 * 2.63%*
Amean fault-both-18 7351.11 ( 0.00%) 6950.51 * 5.45%*
Amean fault-both-24 9059.30 ( 0.00%) 9159.99 * -1.11%*
Amean fault-both-30 10685.68 ( 0.00%) 11399.02 * -6.68%*
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
---
Hi Andrew, please use this patch to replace below 2 old patches. Thanks.
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/commit/?h=mm-everything-2024-02-20-04-19&id=cb30899d456d64fb83ee3e3d95cd9fbb18735d87
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/commit/?h=mm-everything-2024-02-20-04-19&id=65713d1c4fc498d35dc1f7c1234ef815aa128429
Changes from v2:
- Add acked tag from Mel.
- Fix the mm_compaction_migratepages trace event.
Changes from v1:
- Rebased on the latest mm-unstable branch.
---
include/trace/events/compaction.h | 6 +++---
mm/compaction.c | 12 ++++++++++--
2 files changed, 13 insertions(+), 5 deletions(-)
diff --git a/include/trace/events/compaction.h b/include/trace/events/compaction.h
index 2b2a975efd20..d05759d18538 100644
--- a/include/trace/events/compaction.h
+++ b/include/trace/events/compaction.h
@@ -78,10 +78,10 @@ DEFINE_EVENT(mm_compaction_isolate_template, mm_compaction_fast_isolate_freepage
#ifdef CONFIG_COMPACTION
TRACE_EVENT(mm_compaction_migratepages,
- TP_PROTO(struct compact_control *cc,
+ TP_PROTO(unsigned int nr_migratepages,
unsigned int nr_succeeded),
- TP_ARGS(cc, nr_succeeded),
+ TP_ARGS(nr_migratepages, nr_succeeded),
TP_STRUCT__entry(
__field(unsigned long, nr_migrated)
@@ -90,7 +90,7 @@ TRACE_EVENT(mm_compaction_migratepages,
TP_fast_assign(
__entry->nr_migrated = nr_succeeded;
- __entry->nr_failed = cc->nr_migratepages - nr_succeeded;
+ __entry->nr_failed = nr_migratepages - nr_succeeded;
),
TP_printk("nr_migrated=%lu nr_failed=%lu",
diff --git a/mm/compaction.c b/mm/compaction.c
index 4494b2914386..218089b29f13 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1798,6 +1798,7 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data)
dst = list_entry(cc->freepages.next, struct folio, lru);
list_del(&dst->lru);
cc->nr_freepages--;
+ cc->nr_migratepages--;
return dst;
}
@@ -1813,6 +1814,7 @@ static void compaction_free(struct folio *dst, unsigned long data)
list_add(&dst->lru, &cc->freepages);
cc->nr_freepages++;
+ cc->nr_migratepages++;
}
/* possible outcome of isolate_migratepages */
@@ -2435,7 +2437,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
unsigned long last_migrated_pfn;
const bool sync = cc->mode != MIGRATE_ASYNC;
bool update_cached;
- unsigned int nr_succeeded = 0;
+ unsigned int nr_succeeded = 0, nr_migratepages;
/*
* These counters track activities during zone compaction. Initialize
@@ -2553,11 +2555,17 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
pageblock_start_pfn(cc->migrate_pfn - 1));
}
+ /*
+ * Record the number of pages to migrate since the
+ * compaction_alloc/free() will update cc->nr_migratepages
+ * properly.
+ */
+ nr_migratepages = cc->nr_migratepages;
err = migrate_pages(&cc->migratepages, compaction_alloc,
compaction_free, (unsigned long)cc, cc->mode,
MR_COMPACTION, &nr_succeeded);
- trace_mm_compaction_migratepages(cc, nr_succeeded);
+ trace_mm_compaction_migratepages(nr_migratepages, nr_succeeded);
/* All pages were either migrated or will be released */
cc->nr_migratepages = 0;
--
2.39.3
