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Wed, 02 Jul 2025 19:40:15 -0700 (PDT) Received: from localhost.localdomain ([210.184.73.204]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-b362cef26dfsm4709952a12.46.2025.07.02.19.40.08 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Wed, 02 Jul 2025 19:40:14 -0700 (PDT) From: Hao Jia To: akpm@linux-foundation.org, yuzhao@google.com, yuanchu@google.com, shakeel.butt@linux.dev, mhocko@kernel.org, lorenzo.stoakes@oracle.com, kinseyho@google.com, hannes@cmpxchg.org, gthelen@google.com, david@redhat.com, axelrasmussen@google.com, zhengqi.arch@bytedance.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hao Jia Subject: [PATCH v2] mm/mglru: Stop try_to_inc_min_seq() if min_seq[type] has not increased Date: Thu, 3 Jul 2025 10:39:46 +0800 Message-Id: <20250703023946.65315-1-jiahao.kernel@gmail.com> X-Mailer: git-send-email 2.39.2 (Apple Git-143) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Hao Jia 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. Suggested-by: Yuanchu Xie Signed-off-by: Hao Jia --- v1 to v2: - Modify commit message to make proof clearer. - Use one bool to detect any increments in min_seq[type], suggested by Yuanchu Xie. Link to v1: https://lore.kernel.org/all/20250630080603.36171-1-jiahao.kernel@gmail.com mm/vmscan.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/mm/vmscan.c b/mm/vmscan.c index d48e8d365502..d5b6924aeb8f 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3919,6 +3919,7 @@ 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); @@ -3935,11 +3936,20 @@ 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; -- 2.34.1