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

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Message-ID: <nohu552nfqkfumrj3zc7akbdrq3bzwexle3i6weyta76dltppv@txizmvtg3swd>
Date: Wed, 4 Jun 2025 09:54:29 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: Vlastimil Babka <vbabka@...e.cz>, Michal Hocko <mhocko@...e.com>, 
	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 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?