linux-kernel - Re: [PATCH] mm: fix the inaccurate memory statistics issue for users

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Message-ID: <d2b76402-7e1a-4b2d-892a-2e8ffe1a37a9@linux.alibaba.com>
Date: Wed, 4 Jun 2025 22:16:18 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Vlastimil Babka <vbabka@...e.cz>, Shakeel Butt <shakeel.butt@...ux.dev>,
 Michal Hocko <mhocko@...e.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, david@...hat.com,
 lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, rppt@...nel.org,
 surenb@...gle.com, donettom@...ux.ibm.com, aboorvad@...ux.ibm.com,
 sj@...nel.org, linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: fix the inaccurate memory statistics issue for users



On 2025/6/4 21:46, Vlastimil Babka wrote:
> On 6/4/25 14:46, Baolin Wang wrote:
>>> Baolin, please run stress-ng command that stresses minor anon page
>>> faults in multiple threads and then run multiple bash scripts which cat
>>> /proc/pidof(stress-ng)/status. That should be how much the stress-ng
>>> process is impacted by the parallel status readers versus without them.
>>
>> Sure. Thanks Shakeel. I run the stress-ng with the 'stress-ng --fault 32
>> --perf -t 1m' command, while simultaneously running the following
>> scripts to read the /proc/pidof(stress-ng)/status for each thread.
> 
> How many of those scripts?

1 script, but will start 32 threads to read each stress-ng thread's 
status interface.

>>   From the following data, I did not observe any obvious impact of this
>> patch on the stress-ng tests when repeatedly reading the
>> /proc/pidof(stress-ng)/status.
>>
>> w/o patch
>> stress-ng: info:  [6891]          3,993,235,331,584 CPU Cycles
>>            59.767 B/sec
>> stress-ng: info:  [6891]          1,472,101,565,760 Instructions
>>            22.033 B/sec (0.369 instr. per cycle)
>> stress-ng: info:  [6891]                 36,287,456 Page Faults Total
>>             0.543 M/sec
>> stress-ng: info:  [6891]                 36,287,456 Page Faults Minor
>>             0.543 M/sec
>>
>> w/ patch
>> stress-ng: info:  [6872]          4,018,592,975,968 CPU Cycles
>>            60.177 B/sec
>> stress-ng: info:  [6872]          1,484,856,150,976 Instructions
>>            22.235 B/sec (0.369 instr. per cycle)
>> stress-ng: info:  [6872]                 36,547,456 Page Faults Total
>>             0.547 M/sec
>> stress-ng: info:  [6872]                 36,547,456 Page Faults Minor
>>             0.547 M/sec
>>
>> =========================
>> #!/bin/bash
>>
>> # Get the PIDs of stress-ng processes
>> PIDS=$(pgrep stress-ng)
>>
>> # Loop through each PID and monitor /proc/[pid]/status
>> for PID in $PIDS; do
>>       while true; do
>>           cat /proc/$PID/status
>> 	usleep 100000
> 
> Hm but this limits the reading to 10 per second? If we want to simulate an
> adversary process, it should be without the sleeps I think?

OK. I drop the usleep, and I still can not see obvious impact.

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