linux-kernel - [PATCH] mm: compaction: include compound page count for scanning in pageblock isolation

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Message-Id: <20220711202806.22296-1-william.lam@bytedance.com>
Date:   Mon, 11 Jul 2022 21:28:06 +0100
From:   William Lam <william.lam@...edance.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     William Lam <william.lam@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] mm: compaction: include compound page count for scanning in pageblock isolation

The number of scanned pages can be lower than the number of isolated
pages when isolating mirgratable or free pageblock. The metric is being
reported in trace event and also used in vmstat.

This behaviour is confusing since currently the count for isolated pages
takes account of compound page but not for the case of scanned pages.
And given that the number of isolated pages(nr_taken) reported in
mm_compaction_isolate_template trace event is on a single-page basis,
the ambiguity when reporting the number of scanned pages can be removed
by also including compound page count.

Signed-off-by: William Lam <william.lam@...edance.com>
---
 mm/compaction.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/compaction.c b/mm/compaction.c
index 1f89b969c12b..1b51cf2d32b6 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -616,6 +616,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
 			break;
 		set_page_private(page, order);
 
+		nr_scanned += isolated - 1;
 		total_isolated += isolated;
 		cc->nr_freepages += isolated;
 		list_add_tail(&page->lru, freelist);
@@ -1101,6 +1102,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 isolate_success_no_list:
 		cc->nr_migratepages += compound_nr(page);
 		nr_isolated += compound_nr(page);
+		nr_scanned += compound_nr(page) - 1;
 
 		/*
 		 * Avoid isolating too much unless this block is being
@@ -1504,6 +1506,7 @@ fast_isolate_freepages(struct compact_control *cc)
 			if (__isolate_free_page(page, order)) {
 				set_page_private(page, order);
 				nr_isolated = 1 << order;
+				nr_scanned += nr_isolated - 1;
 				cc->nr_freepages += nr_isolated;
 				list_add_tail(&page->lru, &cc->freepages);
 				count_compact_events(COMPACTISOLATED, nr_isolated);
-- 
2.30.1 (Apple Git-130)