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Fri, 23 May 2025 10:14:39 GMT Received: from smtpav06.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4B6D75804E; Fri, 23 May 2025 10:14:43 +0000 (GMT) Received: from smtpav06.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id E686E5803F; Fri, 23 May 2025 10:14:38 +0000 (GMT) Received: from li-c18b6acc-24ee-11b2-a85c-81492619bda1.ibm.com (unknown [9.109.215.55]) by smtpav06.wdc07v.mail.ibm.com (Postfix) with ESMTP; Fri, 23 May 2025 10:14:38 +0000 (GMT) Message-ID: Subject: Re: [RFC PATCH] mm: fix the inaccurate memory statistics issue for users From: Aboorva Devarajan To: Baolin Wang , akpm@linux-foundation.org, david@redhat.com, shakeelb@google.com Cc: lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, aboorvad@linux.ibm.com Date: Fri, 23 May 2025 15:44:37 +0530 In-Reply-To: <3dd21f662925c108cfe706c8954e8c201a327550.1747969935.git.baolin.wang@linux.alibaba.com> References: <3dd21f662925c108cfe706c8954e8c201a327550.1747969935.git.baolin.wang@linux.alibaba.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.1 (3.56.1-1.fc42) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: kQ5NL5TDjSwS59MUQidPvcGmYplsemXy X-Authority-Analysis: v=2.4 cv=XOkwSRhE c=1 sm=1 tr=0 ts=68304a96 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=dt9VzEwgFbYA:10 a=SRrdq9N9AAAA:8 a=VnNF1IyMAAAA:8 a=bJgjvqlET6HPnKk_xIcA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNTIzMDA4OCBTYWx0ZWRfX16m2iHnkczm5 iqWKf4LT5TGBLToXASQndjXxXQ6Ro8K0/reUukgZmcsqRcJ2JOYsY6DeKhUvitqSaOCdVG1wr63 xTbjzwAIYAOBKz71jcB/0sz1S88oOnf+Ma66i3jizUy+1b76dWDczWmuncNtB5i3dcvmmUWUI7x D6yBn44cUmW/90yBWRMj1THYJvMN21LqhoxTZ7YJzbVUL9HtOFglWi4HfgKvwwV6/JwUG6h8qWg XYImosgUg1Rvo0KtL782xVgOZAkWAAvszLepySJGdYM1lasj3juNJOnq8jc2jQrnqE/fLu6ExLq Zok0jJCiHEE7t6TgsOjyQNPiFcZo+9MvIY/okR6Gr9DXQZBFsNXVTisrfft75WiuCZQIOd/Mkwi kDugl0gozqeuAfRi5AC5oSfHOGmACe+hdxpripq5VTENh31GJBtjbtTeaPdNJrHaeqODwqo5 X-Proofpoint-GUID: AR63o-4QBzzE29T2gvaQpZWgN0ph5qqw X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.0.736,FMLib:17.12.80.40 definitions=2025-05-23_03,2025-05-22_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1011 malwarescore=0 mlxlogscore=999 bulkscore=0 mlxscore=0 lowpriorityscore=0 adultscore=0 impostorscore=0 suspectscore=0 priorityscore=1501 spamscore=0 phishscore=0 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2505160000 definitions=main-2505230088 On Fri, 2025-05-23 at 11:16 +0800, Baolin Wang wrote: > On some large machines with a high number of CPUs running a 64K 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. >=20 > =C2=A0=C2=A0=C2=A0 PID USER=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 PR=C2=A0 NI=C2= =A0=C2=A0=C2=A0 VIRT=C2=A0=C2=A0=C2=A0 RES=C2=A0=C2=A0=C2=A0 SHR S=C2=A0 %C= PU=C2=A0 %MEM=C2=A0=C2=A0=C2=A0=C2=A0 TIME+ COMMAND > =C2=A0875525 root=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 20=C2=A0=C2=A0 0=C2=A0=C2= =A0 12480=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 0 R= =C2=A0=C2=A0 0.3=C2=A0=C2=A0 0.0=C2=A0=C2=A0 0:00.08 top > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 1 root=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 20=C2= =A0=C2=A0 0=C2=A0 172800=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0 0 S=C2=A0=C2=A0 0.0=C2=A0=C2=A0 0.0=C2=A0=C2=A0 0:04.52 system= d >=20 > The main reason is that the batch size of the percpu counter is quite lar= ge > on these machines, caching a significant percpu value, since converting m= m's > rss stats into percpu_counter by commit f1a7941243c1 ("mm: convert mm's r= ss > stats into percpu_counter"). Intuitively, the batch number should be opti= mized, > but on some paths, performance may take precedence over statistical accur= acy. > Therefore, introducing a new interface to add the percpu statistical coun= t > and display it to users, which can remove the confusion. In addition, thi= s > change is not expected to be on a performance-critical path, so the modif= ication > should be acceptable. >=20 > Signed-off-by: Baolin Wang > --- > =C2=A0fs/proc/task_mmu.c | 14 +++++++------- > =C2=A0include/linux/mm.h |=C2=A0 5 +++++ > =C2=A02 files changed, 12 insertions(+), 7 deletions(-) >=20 > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index b9e4fbbdf6e6..f629e6526935 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -36,9 +36,9 @@ void task_mem(struct seq_file *m, struct mm_struct *mm) > =C2=A0 unsigned long text, lib, swap, anon, file, shmem; > =C2=A0 unsigned long hiwater_vm, total_vm, hiwater_rss, total_rss; > =C2=A0 > - anon =3D get_mm_counter(mm, MM_ANONPAGES); > - file =3D get_mm_counter(mm, MM_FILEPAGES); > - shmem =3D get_mm_counter(mm, MM_SHMEMPAGES); > + anon =3D get_mm_counter_sum(mm, MM_ANONPAGES); > + file =3D get_mm_counter_sum(mm, MM_FILEPAGES); > + shmem =3D get_mm_counter_sum(mm, MM_SHMEMPAGES); > =C2=A0 > =C2=A0 /* > =C2=A0 * Note: to minimize their overhead, mm maintains hiwater_vm and > @@ -59,7 +59,7 @@ void task_mem(struct seq_file *m, struct mm_struct *mm) > =C2=A0 text =3D min(text, mm->exec_vm << PAGE_SHIFT); > =C2=A0 lib =3D (mm->exec_vm << PAGE_SHIFT) - text; > =C2=A0 > - swap =3D get_mm_counter(mm, MM_SWAPENTS); > + swap =3D get_mm_counter_sum(mm, MM_SWAPENTS); > =C2=A0 SEQ_PUT_DEC("VmPeak:\t", hiwater_vm); > =C2=A0 SEQ_PUT_DEC(" kB\nVmSize:\t", total_vm); > =C2=A0 SEQ_PUT_DEC(" kB\nVmLck:\t", mm->locked_vm); > @@ -92,12 +92,12 @@ unsigned long task_statm(struct mm_struct *mm, > =C2=A0 unsigned long *shared, unsigned long *text, > =C2=A0 unsigned long *data, unsigned long *resident) > =C2=A0{ > - *shared =3D get_mm_counter(mm, MM_FILEPAGES) + > - get_mm_counter(mm, MM_SHMEMPAGES); > + *shared =3D get_mm_counter_sum(mm, MM_FILEPAGES) + > + get_mm_counter_sum(mm, MM_SHMEMPAGES); > =C2=A0 *text =3D (PAGE_ALIGN(mm->end_code) - (mm->start_code & PAGE_MASK)= ) > =C2=A0 >> PAGE_SHIFT; > =C2=A0 *data =3D mm->data_vm + mm->stack_vm; > - *resident =3D *shared + get_mm_counter(mm, MM_ANONPAGES); > + *resident =3D *shared + get_mm_counter_sum(mm, MM_ANONPAGES); > =C2=A0 return mm->total_vm; > =C2=A0} > =C2=A0 > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 185424858f23..15ec5cfe9515 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2568,6 +2568,11 @@ static inline unsigned long get_mm_counter(struct = mm_struct *mm, int member) > =C2=A0 return percpu_counter_read_positive(&mm->rss_stat[member]); > =C2=A0} > =C2=A0 > +static inline unsigned long get_mm_counter_sum(struct mm_struct *mm, int= member) > +{ > + return percpu_counter_sum_positive(&mm->rss_stat[member]); > +} > + > =C2=A0void mm_trace_rss_stat(struct mm_struct *mm, int member); > =C2=A0 > =C2=A0static inline void add_mm_counter(struct mm_struct *mm, int member,= long value) Hi Baolin, This patch looks good to me. We observed a similar issue where the generic mm selftest split_huge_page_test failed due to outdated RssAnon values reported in /proc/[pid]/status. ... Without Patch: # ./split_huge_page_test=20 TAP version 13 1..34 Bail out! No RssAnon is allocated before split # Planned tests !=3D run tests (34 !=3D 0) # Totals: pass:0 fail:0 xfail:0 xpass:0 skip:0 error:0 ... With Patch: # ./split_huge_page_test # ./split_huge_page_test=20 TAP version 13 1..34 ... # Totals: pass:11 fail:0 xfail:0 xpass:0 skip:23 error:0 ... While this change may introduce some lock contention, it only affects the task_mem function which is invoked only when reading /proc/[pid]/status. Since this is not on a performance critical path, it will be good to have this change in order to get accurate memory stats. This fix resolves the issue we've seen with split_huge_page_test. Thanks! Reviewed-by: Aboorva Devarajan Tested-by: Aboorva Devarajan