From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 68411221273; Thu, 10 Jul 2025 04:09:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752120564; cv=none; b=bJ/qhOZroU9ve6hZKMhX0kzlf/Dha7GjRNj8nR13BiHJFwLCEhIgga2y5tAGFGD05Xt7foTFWv/JG0l8O9HWFmIhA6Wn+8O1CKWa0g9FFob7lk5Rd/UfX5DXV9U7oWFA17Q2Zm92ojVX3cUz+ZlXZ1WOGZ3mpfFkAhBCc7p3JkU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752120564; c=relaxed/simple; bh=X7odLtwWvTE5dVI69aloxdhWBOIUz837pkbmb+BKzTY=; h=Date:To:From:Subject:Message-Id; b=memZ0FKKkigiqr2sTpkktHYK15pqnSY7JOgdgbtyN8moetEDvnVIDdIHVN6y6nDOUXr8EAmGRXchIc4O0oz7uA01Pgp1m9qJFG0HsDPCy4XFHoGLqecaMvHPaQwzm3XGrILTHFjaWIr0JIe4hvlks+RjBhu67Ml6+i+IzC47Dfo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=CkC+4vBx; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="CkC+4vBx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3F161C4CEE3; Thu, 10 Jul 2025 04:09:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1752120564; bh=X7odLtwWvTE5dVI69aloxdhWBOIUz837pkbmb+BKzTY=; h=Date:To:From:Subject:From; b=CkC+4vBxMZ9IgaPO5fydQAQI86AYcGIqfQxhOWJgXhnPfnkBl/gD0TrRFX9I00Qb+ fU81JcjOudgdmywugFeQraSkK1nOxI1QU79L1AWlEb/ZoAGZUNKgjAkqQbi2pNAqTv lgfLXIbEzG2yFqzP3QM5k0keNs4MQH8KHHxyfY+k= Date: Wed, 09 Jul 2025 21:09:23 -0700 To: mm-commits@vger.kernel.org,vbabka@suse.cz,surenb@google.com,stable@vger.kernel.org,sj@kernel.org,shakeel.butt@linux.dev,rppt@kernel.org,mhocko@suse.com,lorenzo.stoakes@oracle.com,liam.howlett@oracle.com,david@redhat.com,aboorvad@linux.ibm.com,baolin.wang@linux.alibaba.com,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-hotfixes-stable] mm-fix-the-inaccurate-memory-statistics-issue-for-users.patch removed from -mm tree Message-Id: <20250710040924.3F161C4CEE3@smtp.kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: mm: fix the inaccurate memory statistics issue for users has been removed from the -mm tree. Its filename was mm-fix-the-inaccurate-memory-statistics-issue-for-users.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Baolin Wang Subject: mm: fix the inaccurate memory statistics issue for users Date: Thu, 5 Jun 2025 20:58:29 +0800 On some large machines with a high number of CPUs running a 64K pagesize kernel, we found that the 'RES' field is always 0 displayed by the top command for some processes, which will cause a lot of confusion for users. PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 875525 root 20 0 12480 0 0 R 0.3 0.0 0:00.08 top 1 root 20 0 172800 0 0 S 0.0 0.0 0:04.52 systemd The main reason is that the batch size of the percpu counter is quite large on these machines, caching a significant percpu value, since converting mm's rss stats into percpu_counter by commit f1a7941243c1 ("mm: convert mm's rss stats into percpu_counter"). Intuitively, the batch number should be optimized, but on some paths, performance may take precedence over statistical accuracy. Therefore, introducing a new interface to add the percpu statistical count and display it to users, which can remove the confusion. In addition, this change is not expected to be on a performance-critical path, so the modification should be acceptable. In addition, the 'mm->rss_stat' is updated by using add_mm_counter() and dec/inc_mm_counter(), which are all wrappers around percpu_counter_add_batch(). In percpu_counter_add_batch(), there is percpu batch caching to avoid 'fbc->lock' contention. This patch changes task_mem() and task_statm() to get the accurate mm counters under the 'fbc->lock', but this should not exacerbate kernel 'mm->rss_stat' lock contention due to the percpu batch caching of the mm counters. The following test also confirm the theoretical analysis. I run the stress-ng that stresses anon page faults in 32 threads on my 32 cores machine, while simultaneously running a script that starts 32 threads to busy-loop pread each stress-ng thread's /proc/pid/status interface. From the following data, I did not observe any obvious impact of this patch on the stress-ng tests. w/o patch: stress-ng: info: [6848] 4,399,219,085,152 CPU Cycles 67.327 B/sec stress-ng: info: [6848] 1,616,524,844,832 Instructions 24.740 B/sec (0.367 instr. per cycle) stress-ng: info: [6848] 39,529,792 Page Faults Total 0.605 M/sec stress-ng: info: [6848] 39,529,792 Page Faults Minor 0.605 M/sec w/patch: stress-ng: info: [2485] 4,462,440,381,856 CPU Cycles 68.382 B/sec stress-ng: info: [2485] 1,615,101,503,296 Instructions 24.750 B/sec (0.362 instr. per cycle) stress-ng: info: [2485] 39,439,232 Page Faults Total 0.604 M/sec stress-ng: info: [2485] 39,439,232 Page Faults Minor 0.604 M/sec On comparing a very simple app which just allocates & touches some memory against v6.1 (which doesn't have f1a7941243c1) and latest Linus tree (4c06e63b9203) I can see that on latest Linus tree the values for VmRSS, RssAnon and RssFile from /proc/self/status are all zeroes while they do report values on v6.1 and a Linus tree with this patch. Link: https://lkml.kernel.org/r/f4586b17f66f97c174f7fd1f8647374fdb53de1c.1749119050.git.baolin.wang@linux.alibaba.com Fixes: f1a7941243c1 ("mm: convert mm's rss stats into percpu_counter") Signed-off-by: Baolin Wang Reviewed-by: Aboorva Devarajan Tested-by: Aboorva Devarajan Tested-by Donet Tom Acked-by: Shakeel Butt Acked-by: SeongJae Park Acked-by: Michal Hocko Reviewed-by: Vlastimil Babka Cc: David Hildenbrand Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Signed-off-by: Andrew Morton --- fs/proc/task_mmu.c | 14 +++++++------- include/linux/mm.h | 5 +++++ 2 files changed, 12 insertions(+), 7 deletions(-) --- a/fs/proc/task_mmu.c~mm-fix-the-inaccurate-memory-statistics-issue-for-users +++ a/fs/proc/task_mmu.c @@ -36,9 +36,9 @@ void task_mem(struct seq_file *m, struct unsigned long text, lib, swap, anon, file, shmem; unsigned long hiwater_vm, total_vm, hiwater_rss, total_rss; - anon = get_mm_counter(mm, MM_ANONPAGES); - file = get_mm_counter(mm, MM_FILEPAGES); - shmem = get_mm_counter(mm, MM_SHMEMPAGES); + anon = get_mm_counter_sum(mm, MM_ANONPAGES); + file = get_mm_counter_sum(mm, MM_FILEPAGES); + shmem = get_mm_counter_sum(mm, MM_SHMEMPAGES); /* * Note: to minimize their overhead, mm maintains hiwater_vm and @@ -59,7 +59,7 @@ void task_mem(struct seq_file *m, struct text = min(text, mm->exec_vm << PAGE_SHIFT); lib = (mm->exec_vm << PAGE_SHIFT) - text; - swap = get_mm_counter(mm, MM_SWAPENTS); + swap = get_mm_counter_sum(mm, MM_SWAPENTS); SEQ_PUT_DEC("VmPeak:\t", hiwater_vm); SEQ_PUT_DEC(" kB\nVmSize:\t", total_vm); SEQ_PUT_DEC(" kB\nVmLck:\t", mm->locked_vm); @@ -92,12 +92,12 @@ unsigned long task_statm(struct mm_struc unsigned long *shared, unsigned long *text, unsigned long *data, unsigned long *resident) { - *shared = get_mm_counter(mm, MM_FILEPAGES) + - get_mm_counter(mm, MM_SHMEMPAGES); + *shared = get_mm_counter_sum(mm, MM_FILEPAGES) + + get_mm_counter_sum(mm, MM_SHMEMPAGES); *text = (PAGE_ALIGN(mm->end_code) - (mm->start_code & PAGE_MASK)) >> PAGE_SHIFT; *data = mm->data_vm + mm->stack_vm; - *resident = *shared + get_mm_counter(mm, MM_ANONPAGES); + *resident = *shared + get_mm_counter_sum(mm, MM_ANONPAGES); return mm->total_vm; } --- a/include/linux/mm.h~mm-fix-the-inaccurate-memory-statistics-issue-for-users +++ a/include/linux/mm.h @@ -2568,6 +2568,11 @@ static inline unsigned long get_mm_count return percpu_counter_read_positive(&mm->rss_stat[member]); } +static inline unsigned long get_mm_counter_sum(struct mm_struct *mm, int member) +{ + return percpu_counter_sum_positive(&mm->rss_stat[member]); +} + void mm_trace_rss_stat(struct mm_struct *mm, int member); static inline void add_mm_counter(struct mm_struct *mm, int member, long value) _ Patches currently in -mm which might be from baolin.wang@linux.alibaba.com are selftests-khugepaged-fix-the-shmem-collapse-failure.patch selftests-mm-add-shmem-collapse-as-a-default-test-item.patch mm-huge_memory-fix-the-check-for-allowed-huge-orders-in-shmem.patch khugepaged-allow-khugepaged-to-check-all-anonymous-mthp-orders.patch khugepaged-kick-khugepaged-for-enabling-none-pmd-sized-mthps.patch mm-fault-in-complete-folios-instead-of-individual-pages-for-tmpfs.patch