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Message-Id: <994af744828efe3c060128445204a56ab41e3ebb.1706706820.git.baolin.wang@linux.alibaba.com>
Date: Wed, 31 Jan 2024 21:16:26 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: akpm@...ux-foundation.org
Cc: mgorman@...hsingularity.net,
vbabka@...e.cz,
baolin.wang@...ux.alibaba.com,
linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v2] mm: compaction: update the cc->nr_migratepages when allocating or freeing the freepages
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@...ux.alibaba.com>
---
Changes from v1:
- Rebased on the latest mm-unstable branch.
---
mm/compaction.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/mm/compaction.c b/mm/compaction.c
index 055687e6bd17..363c3e49fe80 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1882,6 +1882,7 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data)
if (order)
prep_compound_page(&dst->page, order);
cc->nr_freepages -= 1 << order;
+ cc->nr_migratepages -= 1 << order;
return page_rmappable_folio(&dst->page);
}
@@ -1904,6 +1905,7 @@ static void compaction_free(struct folio *dst, unsigned long data)
list_add(&dst->lru, &cc->freepages[order].pages);
cc->freepages[order].nr_pages++;
cc->nr_freepages += 1 << order;
+ cc->nr_migratepages += 1 << order;
}
/* possible outcome of isolate_migratepages */
--
2.39.3
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