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Message-Id: <20231129104530.63787-1-v-songbaohua@oppo.com>
Date: Wed, 29 Nov 2023 23:45:30 +1300
From: Barry Song <21cnbao@...il.com>
To: akpm@...ux-foundation.org, linux-mm@...ck.org
Cc: david@...hat.com, shikemeng@...weicloud.com, willy@...radead.org,
mgorman@...hsingularity.net, hannes@...xchg.org,
baolin.wang@...ux.alibaba.com, linux-kernel@...r.kernel.org,
Barry Song <v-songbaohua@...o.com>,
Zhanyuan Hu <huzhanyuan@...o.com>
Subject: [RFC PATCH] mm: compaction: avoid fast_isolate_freepages blindly choose improper pageblock
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;
}
}
}
}
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@...o.com>
Signed-off-by: Barry Song <v-songbaohua@...o.com>
---
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);
--
2.34.1
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