From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B8C2D476CFD for ; Fri, 21 Aug 2026 10:26:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787307983; cv=none; b=ZPP7hNkVdWiL0HLy4JoWSwcNsyLUkE7/WULXq3muWQheWcBPeT8QfyWMOo167XrGs7032ccdTzwDIgQ3gQNv/vzCwpuuN7mSLPlJl8HitaQauMQnA3BnqGmIIVdfZm9RIma8Q6Rm1BqTUp3WPAGxj5vchGm/K9YE+r46e78jJFk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787307983; c=relaxed/simple; bh=NTfM7A0OPas8ToSA1xGAmyqVsZi18gdTLUZrgVubmwY=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version:Content-Type; b=A9nWEFyrdcGP9RARPqr6iQzRVl3mfwE+AJbFLuDLAvvzt0A3avd8ygZqaIGujS1ipH8+wrBp/pYGNsSo1Qv2qwuXrlka3MqgvqIBiFHxCnlbSpioRtlKE648w+59xbCEFh5W++lxCCf7F58ubXTr/MFjjiEyk4gT5x6AY6sj4iw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Fbq0d4vM; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Fbq0d4vM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8DCF51F000E9; Fri, 21 Aug 2026 10:26:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787307978; bh=DImEcDtOKUY2rAhijhJNaWF8FQiu+X6BoqAJgd4cEOM=; h=From:To:Cc:Subject:Date; b=Fbq0d4vMNd3d7+s+DE1ZJPxLzlbTpOctIuZyaxcizV+27mCifm8+4C1vLznc8JEZF uq0NQ/BfbbNBz/mi/TW5tUmntUeoOlINBy/VGirTKLHIYdnXwtbA2VsBjMTWlGBQpK 7tDkfkP5PNREGldA/fAlm/LfpEU4EmUfLFzlzCTzieWSxICz9Xo5XIaMnESYdAbKcW lfA8FCIAZ0J4N+FKE9gAterklHs1TXsG+BMvthUZ0keL94EQj4A0opRoq75Vz6mEfX 6wHUG/FFYaTeH67kOJZGJkw4i9j8HpIC/dO26VcFUlvNb5gZ2BRlKC14ZOg0FMCbBR TlFwunhkT59Sg== From: "Barry Song (Xiaomi)" To: akpm@linux-foundation.org, linux-mm@kvack.org Cc: axelrasmussen@google.com, baolin.wang@linux.alibaba.com, baoquan.he@linux.dev, chenridong@xiaomi.com, david@kernel.org, hannes@cmpxchg.org, kasong@tencent.com, lianux.mm@gmail.com, linux-kernel@vger.kernel.org, ljs@kernel.org, lyugaofei@xiaomi.com, mhocko@kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, stevensd@chromium.org, wangzicheng@honor.com, weixugc@google.com, yuanchu@google.com, zhangbo56@xiaomi.com, "Barry Song (Xiaomi)" Subject: [PATCH 0/6] mm/mglru: speed up inc_min_seq() and fix cold/hot inversions Date: Fri, 21 Aug 2026 18:25:32 +0800 Message-Id: <20260821102538.22642-1-baohua@kernel.org> X-Mailer: git-send-email 2.39.3 (Apple Git-146) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This is an aging speedup series split out from the MGLRU swappiness series [1], with the inc_min_seq changes separated to make them easier to review. Currently, inc_min_seq performance is crucial to both the swappiness fix and proactive aging. There are two problems with it: 1. It processes each folio one by one, while many operations can be batched or skipped. For example, a batch of folios can be moved together from the oldest generation to the second-oldest generation, and the associated counting can also be done in batches. 2. It may cause potential cold/hot inversion by placing promoted folios (which have been scanned and found to have young PTEs) behind non-promoted folios. A similar inversion can also occur among non-promoted folios, as tail folios from the oldest generation are placed before head folios when moving them to the second-oldest generation. This series tries to batch operations as much as possible and fix the potential cold/hot inversion by keeping promoted folios ahead of non-promoted folios, while also preserving the order of non-promoted folios when moving them from the oldest generation to the second-oldest generation. Minor issue: inc_min_seq() also counts protected folios improperly, as promoted folios should be skipped, as in sort_folio(). We need a stable workload with a stable number of folios to measure aging and evaluate the speedup in inc_min_seq(). So I asked ChatGPT to generate the microbenchmark below. It ages an LRU vec containing 512 MB of memory 100 times: #define _GNU_SOURCE #include #include #include #include #include #include #include #include #include #define SIZE (512UL * 1024 * 1024) #define LRU_GEN "/sys/kernel/debug/lru_gen" #define TARGET_CGROUP "/system.slice/agetest.scope" #define START_GEN 3 #define END_GEN 103 static long long nsec_diff(const struct timespec *start, const struct timespec *end) { return (end->tv_sec - start->tv_sec) * 1000000000LL + (end->tv_nsec - start->tv_nsec); } static int find_memcg_id(void) { FILE *fp; char line[4096]; int memcg_id; fp = fopen(LRU_GEN, "r"); if (!fp) { perror("fopen lru_gen"); return -1; } while (fgets(line, sizeof(line), fp)) { char *p; if (strncmp(line, "memcg ", 6)) continue; p = line + 6; if (sscanf(p, "%d", &memcg_id) != 1) continue; /* * The memcg path follows the numeric ID. */ p = strchr(p, ' '); if (!p) continue; if (strstr(p, TARGET_CGROUP)) { fclose(fp); return memcg_id; } } fclose(fp); fprintf(stderr, "Cannot find %s\n", TARGET_CGROUP); return -1; } int main(void) { void *addr; int memcg_id; int fd; long long total_ns = 0; /* * mmap 512 MB and touch every page. */ addr = mmap(NULL, SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (addr == MAP_FAILED) { perror("mmap"); return 1; } memset(addr, 0x55, SIZE); printf("mmap: %p, size: %lu MB\n", addr, SIZE / 1024 / 1024); /* * Find the memcg ID automatically. */ memcg_id = find_memcg_id(); if (memcg_id < 0) return 1; printf("memcg: %d (%s)\n", memcg_id, TARGET_CGROUP); printf("aging generation %d -> %d\n", START_GEN, END_GEN); fd = open(LRU_GEN, O_WRONLY); if (fd < 0) { perror("open lru_gen"); return 1; } for (int gen = START_GEN; gen <= END_GEN; gen++) { char buf[128]; int len; struct timespec start, end; long long ns; len = snprintf(buf, sizeof(buf), "+ %d 0 %d\n", memcg_id, gen); clock_gettime(CLOCK_MONOTONIC, &start); if (write(fd, buf, len) != len) { perror("write lru_gen"); close(fd); return 1; } clock_gettime(CLOCK_MONOTONIC, &end); ns = nsec_diff(&start, &end); total_ns += ns; printf("gen %3d: %8.3f ms\n", gen, ns / 1000000.0); fflush(stdout); } close(fd); printf("\nTotal: %.3f ms\n", total_ns / 1000000.0); printf("Average: %.3f ms\n", total_ns / (double)(END_GEN - START_GEN + 1) / 1000000.0); while (1) sleep(1); return 0; } Run the above microbenchmark with: systemd-run --scope --unit=agetest -p MemoryMax=1024M ./agetest I’m seeing inc_min_seq() become significantly faster: W/o patch: Running scope as unit: agetest.scope mmap: 0x72c1b5a00000, size: 512 MB memcg: 12673 (/system.slice/agetest.scope) aging generation 3 -> 103 gen 3: 7.433 ms gen 4: 0.949 ms gen 5: 2.535 ms gen 6: 5.043 ms gen 7: 5.041 ms gen 8: 5.027 ms ... gen 100: 5.035 ms gen 101: 5.011 ms gen 102: 5.029 ms gen 103: 5.056 ms Total: 503.946 ms Average: 4.990 ms W/ patch: Running scope as unit: agetest.scope mmap: 0x7c4b1d200000, size: 512 MB memcg: 12893 (/system.slice/agetest.scope) aging generation 3 -> 103 gen 3: 7.538 ms gen 4: 0.937 ms gen 5: 2.348 ms gen 6: 2.300 ms gen 7: 2.302 ms gen 8: 2.294 ms gen 9: 2.296 ms ... gen 100: 2.292 ms gen 101: 2.307 ms gen 102: 2.293 ms gen 103: 2.293 ms Total: 235.718 ms Average: 2.334 ms The average aging time drops from 4.990 ms to 2.334 ms! [1] https://lore.kernel.org/linux-mm/20260812121658.69965-1-baohua@kernel.org/ Barry Song (Xiaomi) (6): mm/mglru: batch update lrugen->nr_pages in inc_min_seq() mm/mglru: batch update lrugen->protected in inc_min_seq() mm/mglru: enhance cold/hot inversion handling in inc_min_seq() mm/mglru: exclude folios promoted by aging from protected in inc_min_seq() mm/mglru: move folios from oldest gen to second-oldest gen from head to tail mm/mglru: batch move folios to the second-oldest gen's LRU mm/vmscan.c | 98 +++++++++++++++++++++++++++++++++++++++++++---------- 1 file changed, 80 insertions(+), 18 deletions(-) -- 2.34.1