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AKwUvBwtolgw9syp/YwK05RwDQC56mqgBH4yMLjRpkHHG5HiIkHLF+PvO8YGS0wtHh06XYM0nHteFhhCPg==@kvack.org X-Gm-Message-State: AFq9FYLoYT/8TRCqLj86RYC45y7wrUderHzwOFqT5OUtwo3T19mHshHE PA/HyH+vV3kO4DmX4miTZcLgpBp+QFb83KhBmQekuZpLpRoKc+reOO9Fk1F+ySXJYzwob9DInsA MnqlQiHQoOBvevA== X-Received: from plbjy7.prod.google.com ([2002:a17:903:42c7:b0:2e8:1305:c8e1]) (user=rohitner job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90a:d44b:b0:3a8:e1e:3390 with SMTP id 98e67ed59e1d1-3ab3afd49c9mr9663138a91.56.1791864037283; Mon, 12 Oct 2026 21:00:37 -0700 (PDT) Date: Tue, 13 Oct 2026 04:00:34 +0000 Mime-Version: 1.0 X-Mailer: git-send-email 2.56.0.385.gd3acb90ef8-goog Message-ID: <20261013040034.3919469-1-rohitner@google.com> Subject: [PATCH] mm/memcontrol: log userspace OOM wait entry and completion From: Rohit Ner To: Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Andrew Morton Cc: Muchun Song , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Rohit Ner Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: ADFFB140003 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 4k6y4jz7oaux88cse6xby9oydrzgg846 X-HE-Tag: 1791864038-77172 X-HE-Meta: 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 iKbpKTP5 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: When a memory cgroup hits its limit with memory.oom_control oom_kill_disable configured, mem_cgroup_oom_synchronize() puts the faulting task to sleep on memcg_oom_waitq and notifies userspace OOM handlers to reclaim memory, enlarge limits, or terminate tasks. On platforms where userspace is severely stalled under memory pressure before a hardware or software watchdog reset, no kernel breadcrumb is currently emitted when a memcg enters or exits this userspace OOM wait. Log rate-limited KERN_ERR messages (pr_err_ratelimited) upon entering and completing the userspace OOM wait in mem_cgroup_oom_synchronize(), including the memcg path, memory usage/limit/unevictable stats, elapsed waited_ms, and whether the task exited due to a fatal signal. Signed-off-by: Rohit Ner --- mm/memcontrol-v1.c | 49 +++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 48 insertions(+), 1 deletion(-) diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c index 05ef55cae..7832ce11f 100644 --- a/mm/memcontrol-v1.c +++ b/mm/memcontrol-v1.c @@ -91,6 +91,12 @@ struct mem_cgroup_event { #define MEMFILE_TYPE(val) ((val) >> 16 & 0xffff) #define MEMFILE_ATTR(val) ((val) & 0xffff) +#define MEMCG_OOM_WAIT_PATH_LEN 128 +#define MEMCG_OOM_STAGE_ENTER "enter" +#define MEMCG_OOM_STAGE_RECOVERED "recovered" +#define MEMCG_OOM_STAGE_KILLED "killed" +#define MEMCG_OOM_UNKNOWN_PATH "" + enum { RES_USAGE, RES_LIMIT, @@ -1372,6 +1378,34 @@ void memcg1_oom_recover(struct mem_cgroup *memcg) __wake_up(&memcg_oom_waitq, TASK_NORMAL, 0, memcg); } +/** + * memcg1_log_oom_wait - Log memcg userspace OOM wait entry and completion + * @memcg: The memory cgroup experiencing the userspace OOM wait + * @stage: Lifecycle stage string ("enter", "recovered", or "killed") + * @waited_ms: Elapsed time spent waiting on memcg_oom_waitq in milliseconds + * @killed: Whether the waiting task woke with a fatal signal pending + * + * Emits a rate-limited KERN_ERR message so that memcg userspace OOM handler + * stalls are captured on serial consoles even when booted with quiet + * (console_loglevel=4) and preserved in dmesg. + */ +static void memcg1_log_oom_wait(struct mem_cgroup *memcg, const char *stage, + unsigned int waited_ms, bool killed) +{ + char cgrp_path[MEMCG_OOM_WAIT_PATH_LEN]; + u64 usage_kb = K((u64)page_counter_read(&memcg->memory)); + u64 limit_kb = K((u64)READ_ONCE(memcg->memory.max)); + u64 unevictable_kb = K((u64)memcg_page_state(memcg, NR_UNEVICTABLE)); + + if (cgroup_path(memcg->css.cgroup, cgrp_path, sizeof(cgrp_path)) < 0) + strscpy(cgrp_path, MEMCG_OOM_UNKNOWN_PATH, sizeof(cgrp_path)); + + pr_err_ratelimited("memcg_oom_wait: stage=%s cgroup=%s comm=%s pid=%d usage_kb=%llu limit_kb=%llu unevictable_kb=%llu waited_ms=%u killed=%d\n", + stage, cgrp_path, current->comm, current->pid, + usage_kb, limit_kb, unevictable_kb, + waited_ms, killed); +} + /** * mem_cgroup_oom_synchronize - complete memcg OOM handling * @handle: actually kill/wait or just clean up the OOM state @@ -1393,6 +1427,7 @@ bool mem_cgroup_oom_synchronize(bool handle) { struct mem_cgroup *memcg = current->memcg_in_oom; struct oom_wait_info owait; + unsigned long start_jiffies = 0; bool locked; /* OOM is global, do not handle */ @@ -1413,10 +1448,22 @@ bool mem_cgroup_oom_synchronize(bool handle) locked = mem_cgroup_oom_trylock(memcg); - if (locked) + if (locked) { + start_jiffies = jiffies; + memcg1_log_oom_wait(memcg, MEMCG_OOM_STAGE_ENTER, 0, false); mem_cgroup_oom_notify(memcg); + } schedule(); + if (locked) { + bool killed = fatal_signal_pending(current); + + memcg1_log_oom_wait(memcg, + killed ? MEMCG_OOM_STAGE_KILLED : + MEMCG_OOM_STAGE_RECOVERED, + jiffies_to_msecs(jiffies - start_jiffies), + killed); + } mem_cgroup_unmark_under_oom(memcg); finish_wait(&memcg_oom_waitq, &owait.wait); -- 2.56.0.385.gd3acb90ef8-goog