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

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Message-ID: <aEE6DW-Gjv95eBTj@tiehlicka>
Date: Thu, 5 Jun 2025 08:32:45 +0200
From: Michal Hocko <mhocko@...e.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: Shakeel Butt <shakeel.butt@...ux.dev>, Vlastimil Babka <vbabka@...e.cz>,
	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 Thu 05-06-25 08:48:07, Baolin Wang wrote:
> 
> 
> On 2025/6/5 00:54, Shakeel Butt wrote:
> > On Wed, Jun 04, 2025 at 10:16:18PM +0800, Baolin Wang wrote:
> > > 
> > > 
> > > 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
> > 
> > Is the above with 32 non-sleeping parallel reader scripts?
> 
> Yes.

Thanks, this seems much more representative. Please update the changelog
with this. With that feel free to add
Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!

-- 
Michal Hocko
SUSE Labs