linux-kernel - Re: [PATCH v2] mm: vmstat: fix /proc/sys/vm/stat

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Message-ID: <YDcDAOxKXSopVe3b@carbon.dhcp.thefacebook.com>
Date:   Wed, 24 Feb 2021 17:53:04 -0800
From:   Roman Gushchin <guro@...com>
To:     Hugh Dickins <hughd@...gle.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>, <linux-mm@...ck.org>,
        <kernel-team@...com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mm: vmstat: fix /proc/sys/vm/stat_refresh generating
 false warnings

On Tue, Feb 23, 2021 at 11:24:23PM -0800, Hugh Dickins wrote:
> On Thu, 6 Aug 2020, Andrew Morton wrote:
> > On Thu, 6 Aug 2020 16:38:04 -0700 Roman Gushchin <guro@...com> wrote:
> 
> August, yikes, I thought it was much more recent.
> 
> > 
> > > it seems that Hugh and me haven't reached a consensus here.
> > > Can, you, please, not merge this patch into 5.9, so we would have
> > > more time to find a solution, acceptable for all?
> > 
> > No probs.  I already had a big red asterisk on it ;)
> 
> I've a suspicion that Andrew might be tiring of his big red asterisk,
> and wanting to unload
> mm-vmstat-fix-proc-sys-vm-stat_refresh-generating-false-warnings.patch
> mm-vmstat-fix-proc-sys-vm-stat_refresh-generating-false-warnings-fix.patch
> mm-vmstat-fix-proc-sys-vm-stat_refresh-generating-false-warnings-fix-2.patch
> into 5.12.
> 
> I would prefer not, and reiterate my Nack: but no great harm will
> befall the cosmos if he overrules that, and it does go through to
> 5.12 - I'll just want to revert it again later.  And I do think a
> more straightforward way of suppressing those warnings would be just
> to delete the code that issues them, rather than brushing them under
> a carpet of overtuning.

I'm actually fine with either option. My only concern is that if somebody
will try to use the hugetlb_cma boot option AND /proc/sys/vm/stat_refresh
together, they will get a false warning and report them to mm@ or will
waste their time trying to debug a non-existing problem. It's not the end
of the world.
We can also make the warning conditional on CONFIG_DEBUG_VM, for example.

Please, let me know what's your preferred way to go forward.

Thanks!