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Fri, 18 Sep 2026 11:02:57 -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, corbet@lwn.net, hughd@google.com, baolin.wang@linux.alibaba.com, tj@kernel.org, mkoutny@suse.com, skhan@linuxfoundation.org, kunwu.chan@linux.dev, kernel-team@meta.com, nphamcs@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, cgroups@vger.kernel.org Subject: [PATCH v5 09/11] mm, swap: add debugfs counters for vswap Date: Fri, 18 Sep 2026 11:02:39 -0700 Message-ID: <20260918180241.3424851-10-nphamcs@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260918180241.3424851-1-nphamcs@gmail.com> References: <20260918180241.3424851-1-nphamcs@gmail.com> Precedence: bulk X-Mailing-List: linux-doc@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: virtual swap slots (pages) currently allocated * alloc_reject: cumulative pages that failed to get a vswap slot Signed-off-by: Nhat Pham --- mm/swapfile.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/mm/swapfile.c b/mm/swapfile.c index 3c3fc3b87b9b..cf07d87d2301 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -7,6 +7,7 @@ */ #include +#include #include #include #include @@ -142,6 +143,7 @@ static DEFINE_PER_CPU(struct percpu_vswap_cluster, percpu_vswap_cluster) = { .lock = INIT_LOCAL_LOCK(), }; +static atomic_long_t vswap_alloc_reject = ATOMIC_LONG_INIT(0); static void vswap_mark_cache_only(struct swap_cluster_info *ci, unsigned int ci_off); static void vswap_clear_cache_only(struct swap_cluster_info *ci, @@ -1996,6 +1998,7 @@ static bool vswap_alloc(struct folio *folio) this_cpu_write(percpu_vswap_cluster.offset[order], SWAP_ENTRY_INVALID); local_unlock(&percpu_vswap_cluster.lock); + atomic_long_add(folio_nr_pages(folio), &vswap_alloc_reject); return false; } @@ -4827,9 +4830,25 @@ early_param("vswap", early_vswap); /* vswap does no IO on its own. */ static const struct swap_ops vswap_ops = { }; +static int vswap_used_get(void *data, u64 *val) +{ + *val = swap_usage_in_pages(vswap_si); + return 0; +} +DEFINE_DEBUGFS_ATTRIBUTE(vswap_used_fops, vswap_used_get, NULL, "%llu\n"); + +static int vswap_alloc_reject_get(void *data, u64 *val) +{ + *val = atomic_long_read(&vswap_alloc_reject); + return 0; +} +DEFINE_DEBUGFS_ATTRIBUTE(vswap_alloc_reject_fops, vswap_alloc_reject_get, NULL, + "%llu\n"); + static int __init vswap_init(void) { struct swap_info_struct *si; + struct dentry *root; unsigned long maxpages; int err; @@ -4881,6 +4900,12 @@ static int __init vswap_init(void) mutex_unlock(&swapon_mutex); vswap_si = si; + + root = debugfs_create_dir("vswap", NULL); + debugfs_create_file("used", 0444, root, NULL, &vswap_used_fops); + debugfs_create_file("alloc_reject", 0444, root, NULL, + &vswap_alloc_reject_fops); + pr_info("vswap: created virtual swap device (%lu pages)\n", maxpages); /* Last: everything above must be visible before routing starts. */ -- 2.53.0-Meta