[tip: sched/core] sched/numa: Document vma_numab_state fields

[tip-bot2 for Mel Gorman]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     9ae5c00ea2e600a8b823f9b95606dd244f3096bf
Gitweb:        https://git.kernel.org/tip/9ae5c00ea2e600a8b823f9b95606dd244f3096bf
Author:        Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
AuthorDate:    Tue, 10 Oct 2023 09:31:38 +01:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 10 Oct 2023 11:10:00 +02:00

sched/numa: Document vma_numab_state fields

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
---
 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 36c5b43..d7f042e 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];
 };