Commit 526660b9 authored by Hao Jia's avatar Hao Jia Committed by Andrew Morton
Browse files

mm/mglru: stop try_to_inc_min_seq() if min_seq[type] has not increased 

In try_to_inc_min_seq(), if min_seq[type] has not increased.  In other
words, min_seq[type] == lrugen->min_seq[type].  Then we should return
directly to avoid unnecessary overhead later.

Corollary: If min_seq[type] of both anonymous and file is not increased,
try_to_inc_min_seq() will fail.

Proof:
It is known that min_seq[type] has not increased, that is, min_seq[type]
is equal to lrugen->min_seq[type], then the following:

case 1: min_seq[type] has not been reassigned and changed before
judgment min_seq[type] <= lrugen->min_seq[type].
Then the subsequent min_seq[type] <= lrugen->min_seq[type] judgment
will always be true.

case 2: min_seq[type] is reassigned to seq, before judgment
min_seq[type] <= lrugen->min_seq[type].
Then at least the condition of min_seq[type] > seq must be met
before min_seq[type] will be reassigned to seq.
That is to say, before the reassignment, lrugen->min_seq[type] > seq
is met, and then min_seq[type] = seq.
Then the following min_seq[type](seq) <= lrugen->min_seq[type] judgment
is always true.

Therefore, in try_to_inc_min_seq(), If min_seq[type] of both anonymous
and file is not increased, we can return false directly to avoid
unnecessary overhead.

Link: https://lkml.kernel.org/r/20250703023946.65315-1-jiahao.kernel@gmail.com


Signed-off-by: default avatarHao Jia <jiahao1@lixiang.com>
Suggested-by: default avatarYuanchu Xie <yuanchu@google.com>
Reviewed-by: default avatarAxel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kinsey Ho <kinseyho@google.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 9989db9f

mm/vmscan.c

+10 −0
Original line number Diff line number Diff line
@@ -3921,6 +3921,7 @@ static bool try_to_inc_min_seq(struct lruvec *lruvec, int swappiness) 
{

	int gen, type, zone;

	bool success = false;

	bool seq_inc_flag = false;

	struct lru_gen_folio *lrugen = &lruvec->lrugen;

	DEFINE_MIN_SEQ(lruvec);
@@ -3937,11 +3938,20 @@ static bool try_to_inc_min_seq(struct lruvec *lruvec, int swappiness) 
			}



			min_seq[type]++;

			seq_inc_flag = true;

		}

next:

		;

	}



	/*

	 * If min_seq[type] of both anonymous and file is not increased,

	 * we can directly return false to avoid unnecessary checking

	 * overhead later.

	 */

	if (!seq_inc_flag)

		return success;



	/* see the comment on lru_gen_folio */

	if (swappiness && swappiness <= MAX_SWAPPINESS) {

		unsigned long seq = lrugen->max_seq - MIN_NR_GENS;