From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f196.google.com (mail-pg1-f196.google.com [209.85.215.196]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CC6663F8254 for ; Mon, 29 Jun 2026 09:07:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.196 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782724072; cv=none; b=X10yk/j/8XY2JfVhuVYoZU5Rd3nHjnG0+K1F8Vlx/twKLsb2SoYcv3HfHs87BCVVYHoHDYnQZaIkrfUIJUyNrFmuGf1sns9Jdn8qacgEonGVq/jlB24RTO2HnYbcmO/VZBq2WdTaUltC3LTIOb0jBGQhgI+nAaxoMi+lSaaFFAo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782724072; c=relaxed/simple; bh=QkpYU2x6d5CTRAQnAvLOpdP6PC0148ML6LlO38w3JO0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=oyV/RbRO6ydNsTgyDo4za52LKw3tdLEX0IBYpngeZ9jlswNrvv6PR0LNwykPt3rX602DndPGHVcFEXaiCaweeJ6cu9fbFOXxE9YnK+av5Vo7N2NQ+JaR6xTyQbWXH0PV7GvN6lD565ufkOvhXrHnwdvIDK3Z9YpjhMsj7Ze4wH4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=CtKnNUlG; arc=none smtp.client-ip=209.85.215.196 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="CtKnNUlG" Received: by mail-pg1-f196.google.com with SMTP id 41be03b00d2f7-c9aaa90a791so152371a12.3 for ; Mon, 29 Jun 2026 02:07:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1782724070; x=1783328870; darn=lists.linux.dev; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=83HbAI6qOdVU1QL6jhPAqEWUlv3tiZPtQ6kqfm9JAYo=; b=CtKnNUlGHBeBkJQYawVU1Bz5CANpDlzQY7kHcVPo0z4y9ecdbtCvnFSOwxcRKI99mq rrPt63QKhHgJ3Cmeax0LbwL/3QjDG0eJa+STZgIkwKO54ItX50VF/fo93D6P8bwKrRJg WahRcusHoHyKx3Bfl0TjaOku+sFIG16M+lgcoOYIyEkfKAs7kvSUg6Zjg/SIgGfzKvq7 AM/o9ceR3kern8uBSow8BWbbcJ/23ZWDXPIClePn2WTQw2pJMWp8zDXAgZwFaG+s/QPN PYp6y0TgqDbLPDPuW7DYZVp4Dqj/ELySR8Ik+p29efroZiEjK8R/SyNXbPuZXRgl5OKX ztMw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1782724070; x=1783328870; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=83HbAI6qOdVU1QL6jhPAqEWUlv3tiZPtQ6kqfm9JAYo=; b=OItV7pJqicHYf8CE19ztIp8kaBTIatm0grl65j5iACs5uAKn1VPPXBW1Iu3x6LYO1E 5gDNESCmV3HvfU53aNZQCO0dmfnxKoxv2kzTfEovJ1Y5gBNET4nyyMn052q2B9TbDySD groZUQb2cQsZrRvTvAYjc+mpqzd6GEzzQmnOQ3hRhQHEWdtEv9f//ODpCS1e6iBhCygg 3zNUzhnKuWJCQKFCMidTuHPXv4etsTLqzzt/6O8y2xEgd2wxvAlha6pFBD8dRIG6Pcke idOpsc8gnvCzqeV06kUyOSCesOZDlHRDuEzmfw2p5kdEk3ISFNA9q+NbxOL1ToW/rGu5 5H4g== X-Forwarded-Encrypted: i=1; AFNElJ9dQmVCAQVI/D9FoOGCehQu+0ShlEqu4KjfbPNe2+EWDhMYrH+XerurMQIwSUloSCYKdo2XOZlYLR19YmiUdg==@lists.linux.dev X-Gm-Message-State: AOJu0Yzf/OiGrHXe7Hbe6V50n6iN7PxWPBDcrStBAH8yTBkLXSjsNb3g j+1i6yBGhnxg+j+Bg8Eh8rbdQXxk6TNlwKhMNiCLJZKbaR7uoCNui/Pb X-Gm-Gg: AfdE7cli1MCXeLbi857vLXXAN9RA3DM3YIxoQHMd34cqLX4q1niVOwFO4lEmGN+5p8z UkxegJIYKn+iy6NR8XK9O/Tu1s4DcU3ekgS/iaeso/RA/azEjEU/t0PcOy8rIRVE1BRO7IKtNsA maCDqT6KU4ol6nXIWkrZ9wFnKyXpZ2xoxnsptoKngeq6ly97oidC4Je6ieJ8yJD+QAbNaGPIkD8 SpHdwvcP/UN84mZPteBtEXzB0LKrBfoMgnx+Q3V+TUF6ZqWRTvEGJ+V8IfTlnpXBXSj9W5eEI7A A+080YY/DJcLLYGCxph+hJmywvWnoy+mVT55VjaKSFFV/heVUVXPHa+Cp6LJ4RbyV/QUu2HbIrr L/2oXF98udvVefe//Jkdf/r5++gyg7sVsNVteruAVVn3jzESpxflZibbPxJvO44yFZikSdHT4OI ebAQ35/DlhK4kEBXCYJFo5 X-Received: by 2002:a05:6a20:3d21:b0:3b4:85db:1be8 with SMTP id adf61e73a8af0-3bd4af22a37mr16709071637.36.1782724069917; Mon, 29 Jun 2026 02:07:49 -0700 (PDT) Received: from [10.125.112.20] ([210.184.73.204]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c92bc1df037sm7189768a12.17.2026.06.29.02.07.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 29 Jun 2026 02:07:48 -0700 (PDT) Message-ID: <05d7369e-341c-49f4-ae13-df3d0ad930d7@gmail.com> Date: Mon, 29 Jun 2026 17:07:36 +0800 Precedence: bulk X-Mailing-List: linux-rt-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 1/3] mm/compaction: skip isolate mlocked folios when compact_unevictable_allowed=0 To: Alexander Krabler , "Vlastimil Babka (SUSE)" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "linux-trace-kernel@vger.kernel.org" , "linux-rt-devel@lists.linux.dev" Cc: "akpm@linux-foundation.org" , "surenb@google.com" , "mhocko@suse.com" , "jackmanb@google.com" , "hannes@cmpxchg.org" , "ziy@nvidia.com" , "rostedt@goodmis.org" , "mhiramat@kernel.org" , "mathieu.desnoyers@efficios.com" , "david@kernel.org" , "ljs@kernel.org" , "liam@infradead.org" , "rppt@kernel.org" , "bigeasy@linutronix.de" , "clrkwllms@kernel.org" , Hugh Dickins References: <20260604023812.3700316-1-chenwandun1@gmail.com> <20260604023812.3700316-2-chenwandun1@gmail.com> <969cb14b-5b8b-48e6-add6-4dd13101dd89@kernel.org> <040788a9-e0d5-478e-bb48-3d22b8b41020@gmail.com> Content-Language: en-US From: Wandun In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 6/26/26 21:42, Alexander Krabler wrote: > On 6/26/26 11:38, Wandun wrote: >> On 6/26/26 16:45, Alexander Krabler wrote: >>> However, we were not able to reproduce the actual race >>> (mlockall() process waiting on a migration PTE), >>> not in the past, not now. Might be hard to trigger that race. >> >> Not hard to trigger that case, I added a debug message, such as below, >> lots of messages occur in a few second. >> >> diff --cc mm/memory.c >> index ff338c2abe92,ff338c2abe92..6552b3b14f78 >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@@ -4768,6 -4768,6 +4768,8 @@@ vm_fault_t do_swap_page(struct vm_faul >> if (softleaf_is_migration(entry)) { >> migration_entry_wait(vma->vm_mm, vmf->pmd, >> vmf->address); >> + if (!strcmp(current->comm, "repro")) >> + pr_err("============== hit ================\n"); >> } else if (softleaf_is_device_exclusive(entry)) { >> vmf->page = softleaf_to_page(entry); >> ret = remove_device_exclusive_entry(vmf); > > I have a kprobe on migration_entry_wait set and logged into a ftrace buffer > (including kernel stacktrace). > Yes, this function is hit, but only inside the mmap-syscall, which is okay, > memory allocation is not realtime-safe. > > repro-2090 [002] d.... 811.129549: frt_migration_entry_wait: (migration_entry_wait+0x0/0x100) > repro-2090 [002] d.... 811.129553: > => migration_entry_wait > => __handle_mm_fault > => handle_mm_fault > => __get_user_pages > => populate_vma_page_range > => __mm_populate > => vm_mmap_pgoff > => ksys_mmap_pgoff > => __arm64_sys_mmap > => el0_svc_common.constprop.0 > => do_el0_svc > => el0_svc > => el0t_64_sync_handler > => el0t_64_sync > > The original race was an instruction abort interrupt out of nothing due > to the migration PTE set by kcompactd. > And these kind of races I see quite often on non mlockall()-processes, > but can't reproduce on memory locked processes. > > Example: > podman-832 [000] d.... 812.447820: frt_migration_entry_wait: (migration_entry_wait+0x0/0x100) > podman-832 [000] d.... 812.447823: > => migration_entry_wait > => __handle_mm_fault > => handle_mm_fault > => do_page_fault > => do_translation_fault > => do_mem_abort > => el0_da > => el0t_64_sync_handler > => el0t_64_sync Hi, Alexander >From the perspective of the root cause, there is no fundamental difference between these two call stacks. I modified the reproduction program, and it can still reproduce the situation of the second call stack (although it doesn't occur as frequently). The complete reproduction program is as follows: #define _GNU_SOURCE #include #include #include #include #include #include #include #define PAGE_SIZE 4096 #define NR_PAGES 10000 static void *worker_fn(void *arg) { int fd = (long)arg; size_t len = NR_PAGES * PAGE_SIZE; while (1) { if (ftruncate(fd, 0) < 0) {} if (ftruncate(fd, len) < 0) {} char *p = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); if (p == MAP_FAILED) continue; mlockall(MCL_ONFAULT | MCL_FUTURE); for (int i = 0; i < NR_PAGES; i++) { for (int j = 0; j < PAGE_SIZE; j++) { p[i * PAGE_SIZE + j] = 1; } } usleep(200); munmap(p, len); } return NULL; } static void *compact_fn(void *arg) { (void)arg; int fd = open("/proc/sys/vm/compact_memory", O_WRONLY); if (fd < 0) return NULL; while (1) { if (write(fd, "1", 1) < 0) {} usleep(5000); } } int main(void) { int nproc = sysconf(_SC_NPROCESSORS_ONLN); if (nproc < 1) nproc = 1; int *fds = calloc((size_t)nproc, sizeof(int)); if (!fds) return 1; size_t len = NR_PAGES * PAGE_SIZE; for (int i = 0; i < nproc; i++) { char path[64]; snprintf(path, sizeof(path), "./repro_%d.dat", i); unlink(path); fds[i] = open(path, O_RDWR | O_CREAT, 0600); if (fds[i] < 0) return 1; if (ftruncate(fds[i], len) < 0) return 1; } printf("repro: %d workers, %d pages, Ctrl-C to stop\n", nproc, NR_PAGES); pthread_t compact; pthread_create(&compact, NULL, compact_fn, NULL); pthread_t *threads = calloc((size_t)nproc, sizeof(pthread_t)); for (int i = 0; i < nproc; i++) pthread_create(&threads[i], NULL, worker_fn, (void *)(long)fds[i]); pthread_join(compact, NULL); return 0; } > > Thanks, > Alexander > > -- > > KUKA Deutschland GmbH Board of Directors: Michael Jürgens (Chairman), Johan Naten, Hui Zhang Registered Office: Augsburg HRB 14914 > > This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of contents of this e-mail is strictly forbidden. > > Please consider the environment before printing this e-mail.