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Mon, 30 Jun 2025 01:06:15 -0700 (PDT) Received: from localhost.localdomain ([210.184.73.204]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-b34e3023a11sm6525673a12.25.2025.06.30.01.06.10 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Mon, 30 Jun 2025 01:06:15 -0700 (PDT) From: Hao Jia To: akpm@linux-foundation.org, hannes@cmpxchg.org, yuzhao@google.com, kinseyho@google.com, david@redhat.com, mhocko@kernel.org, zhengqi.arch@bytedance.com, shakeel.butt@linux.dev, lorenzo.stoakes@oracle.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hao Jia Subject: [PATCH] mm/mglru: Stop try_to_inc_min_seq() if the oldest generation LRU lists are not empty Date: Mon, 30 Jun 2025 16:06:03 +0800 Message-Id: <20250630080603.36171-1-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 the oldest generation of LRU lists (anonymous and file) are not empty. Then we should return directly to avoid unnecessary subsequent overhead. Corollary: If the lrugen->folios[gen][type][zone] lists of both anonymous and file are not empty, try_to_inc_min_seq() will fail. Proof: Taking LRU_GEN_ANON as an example, consider the following two cases: Case 1: min_seq[LRU_GEN_ANON] <= seq (seq is lrugen->max_seq - MIN_NR_GENS) Since min_seq[LRU_GEN_ANON] has not increased, so min_seq[LRU_GEN_ANON] is still equal to lrugen->min_seq[LRU_GEN_ANON]. Therefore, in the following judgment: min_seq[LRU_GEN_ANON] <= lrugen->min_seq[LRU_GEN_ANON] is always true. So, we will not increase the seq of the oldest generation of anonymous, and try_to_inc_min_seq() will return false. case 2: min_seq[LRU_GEN_ANON] > seq (seq is lrugen->max_seq - MIN_NR_GENS) If min_seq[LRU_GEN_ANON] > seq, that is, lrugen->min_seq[LRU_GEN_ANON] > seq Then min_seq[LRU_GEN_ANON] is assigned seq. Therefore, in the following judgment: min_seq[LRU_GEN_ANON] (seq) <= lrugen->min_seq[LRU_GEN_ANON] is always true. So, we will not update the oldest generation seq of anonymous, and try_to_inc_min_seq() will return false. It is similar for LRU_GEN_FILE. Therefore, in try_to_inc_min_seq(), if the oldest generation LRU lists (anonymous and file) are not empty, in other words, min_seq[type] has not increased. we can directly return false to avoid unnecessary checking overhead later. Signed-off-by: Hao Jia --- mm/vmscan.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/mm/vmscan.c b/mm/vmscan.c index f8dfd2864bbf..3ba63d87563f 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3928,6 +3928,7 @@ static bool try_to_inc_min_seq(struct lruvec *lruvec, int swappiness) int gen, type, zone; bool success = false; struct lru_gen_folio *lrugen = &lruvec->lrugen; + int seq_inc_flags[ANON_AND_FILE] = {0}; DEFINE_MIN_SEQ(lruvec); VM_WARN_ON_ONCE(!seq_is_valid(lruvec)); @@ -3943,11 +3944,20 @@ static bool try_to_inc_min_seq(struct lruvec *lruvec, int swappiness) } min_seq[type]++; + seq_inc_flags[type] = 1; } next: ; } + /* + * If the oldest generation of LRU lists (anonymous and file) + * are not empty, we can directly return false to avoid unnecessary + * checking overhead later. + */ + if (!seq_inc_flags[LRU_GEN_ANON] && !seq_inc_flags[LRU_GEN_FILE]) + 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