[PATCH 6.6 232/538] sched/numa: Document vma_numab_state fields

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6.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>

[ Upstream commit 9ae5c00ea2e600a8b823f9b95606dd244f3096bf ]

Document the intended usage of the fields.

[ mingo: Reformatted to take less vertical space & tidied it up. ]

Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20231010083143.19593-2-mgorman@xxxxxxxxxxxxxxxxxxx
Stable-dep-of: f22cde4371f3 ("sched/numa: Fix the vma scan starving issue")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 include/linux/mm_types.h | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index ba25777ec0a71..b53a13d15bbae 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -551,8 +551,29 @@ struct vma_lock {
 };
 
 struct vma_numab_state {
+	/*
+	 * Initialised as time in 'jiffies' after which VMA
+	 * should be scanned.  Delays first scan of new VMA by at
+	 * least sysctl_numa_balancing_scan_delay:
+	 */
 	unsigned long next_scan;
+
+	/*
+	 * Time in jiffies when access_pids[] is reset to
+	 * detect phase change behaviour:
+	 */
 	unsigned long next_pid_reset;
+
+	/*
+	 * Approximate tracking of PIDs that trapped a NUMA hinting
+	 * fault. May produce false positives due to hash collisions.
+	 *
+	 *   [0] Previous PID tracking
+	 *   [1] Current PID tracking
+	 *
+	 * Window moves after next_pid_reset has expired approximately
+	 * every VMA_PID_RESET_PERIOD jiffies:
+	 */
 	unsigned long access_pids[2];
 };
 
-- 
2.43.0







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