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From:   Mel Gorman <mgorman@techsingularity.net>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Raghavendra K T <raghavendra.kt@amd.com>,
        K Prateek Nayak <kprateek.nayak@amd.com>,
        Bharata B Rao <bharata@amd.com>,
        Ingo Molnar <mingo@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        Mel Gorman <mgorman@techsingularity.net>
Subject: [PATCH 1/6] sched/numa: Document vma_numab_state fields
Date:   Tue, 10 Oct 2023 09:31:38 +0100
Message-Id: <20231010083143.19593-2-mgorman@techsingularity.net>
In-Reply-To: <20231010083143.19593-1-mgorman@techsingularity.net>
References: <20231010083143.19593-1-mgorman@techsingularity.net>
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Document the intended usage of the fields.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
 include/linux/mm_types.h | 30 +++++++++++++++++++++++++++---
 1 file changed, 27 insertions(+), 3 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 36c5b43999e6..0fe054afc4d6 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -551,9 +551,33 @@ struct vma_lock {
 };
 
 struct vma_numab_state {
-	unsigned long next_scan;
-	unsigned long next_pid_reset;
-	unsigned long access_pids[2];
+	unsigned long next_scan;		/* 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_pid_reset;		/* Time in jiffies when
+						 * access_pids is reset to
+						 * detect phase change
+						 * behaviour.
+						 */
+	unsigned long access_pids[2];		/* 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.
+						 */
 };
 
 /*
-- 
2.35.3