linux-kernel - [RFC PATCH V1 3/6] sched/numa: Remove unconditional scan logic using mm numa_scan

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Date:   Tue, 29 Aug 2023 11:36:11 +0530
From:   Raghavendra K T <raghavendra.kt@....com>
To:     <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
CC:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Mel Gorman" <mgorman@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "David Hildenbrand" <david@...hat.com>, <rppt@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Bharata B Rao <bharata@....com>,
        Aithal Srikanth <sraithal@....com>,
        "kernel test robot" <oliver.sang@...el.com>,
        Raghavendra K T <raghavendra.kt@....com>,
        Sapkal Swapnil <Swapnil.Sapkal@....com>,
        K Prateek Nayak <kprateek.nayak@....com>
Subject: [RFC PATCH V1 3/6] sched/numa: Remove unconditional scan logic using mm numa_scan_seq

It is now redundant after unconditional scans introduced for tasks'
disjoint VMAs.

Also this approach was not considering a rare case where a VMA gets
created after mm numa_scan_seq is greater than two.

Signed-off-by: Raghavendra K T <raghavendra.kt@....com>
---
 kernel/sched/fair.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 23375c10f36e..e26e847a8e26 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2961,14 +2961,6 @@ static bool task_disjoint_vma_select(struct vm_area_struct *vma)
 static bool vma_is_accessed(struct vm_area_struct *vma)
 {
 	unsigned long pids;
-	/*
-	 * Allow unconditional access first two times, so that all the (pages)
-	 * of VMAs get prot_none fault introduced irrespective of accesses.
-	 * This is also done to avoid any side effect of task scanning
-	 * amplifying the unfairness of disjoint set of VMAs' access.
-	 */
-	if (READ_ONCE(current->mm->numa_scan_seq) < 2)
-		return true;
 
 	pids = vma->numab_state->access_pids[0] | vma->numab_state->access_pids[1];
 	return test_bit(hash_32(current->pid, ilog2(BITS_PER_LONG)), &pids);
-- 
2.34.1