Re: [PATCH] lib/test_free_pages: Add basic progress indicators

From: Matthew Wilcox <willy@infradead.org>
To: Mike Rapoport <rppt@kernel.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] lib/test_free_pages: Add basic progress indicators
Date: Mon, 19 Oct 2020 15:05:05 +0100	[thread overview]
Message-ID: <20201019140505.GR20115@casper.infradead.org> (raw)
In-Reply-To: <20201018171252.GA392079@kernel.org>

On Sun, Oct 18, 2020 at 08:12:52PM +0300, Mike Rapoport wrote:
> On Sun, Oct 18, 2020 at 04:01:46PM +0100, Matthew Wilcox wrote:
> > On Sun, Oct 18, 2020 at 04:39:27PM +0200, Geert Uytterhoeven wrote:
> > > Hi Matthew,
> > > 
> > > On Sun, Oct 18, 2020 at 4:25 PM Matthew Wilcox <willy@infradead.org> wrote:
> > > > On Sun, Oct 18, 2020 at 04:04:45PM +0200, Geert Uytterhoeven wrote:
> > > > > The test module to check that free_pages() does not leak memory does not
> > > > > provide any feedback whatsoever its state or progress, but may take some
> > > > > time on slow machines.  Add the printing of messages upon starting each
> > > > > phase of the test, and upon completion.
> > > >
> > > > It's not supposed to take a long time.  Can you crank down that 1000 *
> > > 
> > > It took 1m11s on ARAnyM, running on an i7-8700K.
> > > Real hardware may even take longer.
> > 
> > 71 seconds is clearly too long.  0.7 seconds would be fine, so 10 * 1000
> > would be appropriate, but then that's only 320MB which might not be
> > enough to notice on a modern machine.
> > 
> > > > 1000 to something more appropriate?
> > > 
> > > What would be a suitable value? You do want to see it "leak gigabytes
> > > of memory and probably OOM your system" if something's wrong,
> > > so decreasing the value a lot may not be a good idea?
> > > 
> > > Regardless, if it OOMs, I think you do want to see this happens
> > > while running this test.
> > 
> > How about scaling with the amount of memory on the machine?
> > 
> > This might cause problems on machines with terabytes of memory.
> > Maybe we should cap it at a terabyte?
> 
> On ARAnyM wih 782 MBytes of RAM running on i7-8650U it takes ~1.75
> seconds.

That seems like a somewhat unusual configuration.  I think it's pretty
strange to find an actual m68k with more than 128MB of memory.  I mean,
I can set up my laptop to believe it has 64TB of memory, and this will
run slowly, but I don't think it's any real problem.

> Still, I think adding some verbosity to the test wouldn't hurt ;-)

I prefer the unix philosophy of only emitting messages if something's
wrong.