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Fri, 12 Jun 2026 12:37:49 -0700 (PDT) From: Nhat Pham To: akpm@linux-foundation.org Cc: chrisl@kernel.org, kasong@tencent.com, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, yosry@kernel.org, david@kernel.org, muchun.song@linux.dev, shikemeng@huaweicloud.com, baoquan.he@linux.dev, baohua@kernel.org, youngjun.park@lge.com, chengming.zhou@linux.dev, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, qi.zheng@linux.dev, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, riel@surriel.com, gourry@gourry.net, haowenchao22@gmail.com, kernel-team@meta.com, nphamcs@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org Subject: [RFC PATCH v2 5/7] mm, swap: add debugfs counters for vswap Date: Fri, 12 Jun 2026 12:37:36 -0700 Message-ID: <20260612193738.2183968-6-nphamcs@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260612193738.2183968-1-nphamcs@gmail.com> References: <20260612193738.2183968-1-nphamcs@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add /sys/kernel/debug/vswap/ with two counters: * used: number of virtual swap slots currently allocated * alloc_reject: cumulative count of failed vswap allocations Signed-off-by: Nhat Pham --- mm/swapfile.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/mm/swapfile.c b/mm/swapfile.c index abf6414c01c9..afb118ab8179 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -7,6 +7,7 @@ */ #include +#include #include #include #include @@ -132,6 +133,9 @@ static DEFINE_PER_CPU(struct percpu_swap_cluster, percpu_swap_cluster) = { .lock = INIT_LOCAL_LOCK(), }; +static atomic_t __maybe_unused vswap_used = ATOMIC_INIT(0); +static atomic_t __maybe_unused vswap_alloc_reject = ATOMIC_INIT(0); + #ifdef CONFIG_VSWAP struct percpu_vswap_cluster { unsigned long offset[SWAP_NR_ORDERS]; @@ -2038,11 +2042,13 @@ static bool vswap_alloc(struct folio *folio) if (folio_test_swapcache(folio)) { /* alloc_swap_scan_cluster updated percpu offset already */ local_unlock(&percpu_vswap_cluster.lock); + atomic_add(folio_nr_pages(folio), &vswap_used); return true; } this_cpu_write(percpu_vswap_cluster.offset[order], SWAP_ENTRY_INVALID); local_unlock(&percpu_vswap_cluster.lock); + atomic_add(folio_nr_pages(folio), &vswap_alloc_reject); return false; } #endif @@ -2666,8 +2672,10 @@ void __swap_cluster_free_entries(struct swap_info_struct *si, VM_WARN_ON(ci->count < nr_pages); - if (is_vswap) + if (is_vswap) { __vswap_release_backing(ci, ci_start, nr_pages); + atomic_sub(nr_pages, &vswap_used); + } ci->count -= nr_pages; do { @@ -4849,6 +4857,7 @@ struct swap_info_struct *vswap_si; static int __init vswap_init(void) { struct swap_info_struct *si; + struct dentry *root; unsigned long maxpages; int err; @@ -4878,6 +4887,11 @@ static int __init vswap_init(void) mutex_unlock(&swapon_mutex); vswap_si = si; + + root = debugfs_create_dir("vswap", NULL); + debugfs_create_atomic_t("used", 0444, root, &vswap_used); + debugfs_create_atomic_t("alloc_reject", 0444, root, &vswap_alloc_reject); + pr_info("vswap: created virtual swap device (%lu pages)\n", maxpages); return 0; -- 2.53.0-Meta