linux-kernel - [PATCH] mm, compaction: Indicate when compaction is manually triggered by sysctl

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Message-Id: <20200507215946.22589-1-gpiccoli@canonical.com>
Date:   Thu,  7 May 2020 18:59:46 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...onical.com>
To:     linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        gavin.guo@...onical.com, gpiccoli@...onical.com,
        kernel@...ccoli.net
Subject: [PATCH] mm, compaction: Indicate when compaction is manually triggered by sysctl

Currently we have no way to determine if compaction was triggered
by sysctl write, but this is an interesting information to have,
specially in systems with high uptime that presents lots of
fragmented memory. There's no statistic indicating if compaction
was triggered manually or ran by Linux itself, the vmstat numbers
cannot tell the user this information.

This patch adds a very simple message to kernel log when compaction
is requested through a write to sysctl file, and also it accumulates
the number of previously manual compaction executions. It follows
the approach used by drop_caches.

Signed-off-by: Guilherme G. Piccoli <gpiccoli@...onical.com>
---

This patch was based on linux-next/akpm branch, at d0f3f6070c3a.
Thanks in advance for reviews!
Cheers,

Guilherme

 mm/compaction.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index fb43e731ac31..80e748b0bbb6 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2465,9 +2465,13 @@ int sysctl_compact_memory;
 int sysctl_compaction_handler(struct ctl_table *table, int write,
 			void *buffer, size_t *length, loff_t *ppos)
 {
-	if (write)
+	static unsigned compaction_acct;
+
+	if (write) {
+		pr_info("compact_memory triggered - it already previously ran %u times\n",
+			compaction_acct++);
 		compact_nodes();
-
+	}
 	return 0;
 }

-- 
2.25.2