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From:   Qian Cai <cai@lca.pw>
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Date:   Tue, 2 Jun 2020 00:02:22 -0400
Subject: Re: [PATCH v4 3/4] mm/util.c: remove the VM_WARN_ONCE for vm_committed_as underflow check
Message-Id: <E1703973-38C1-4AFB-94D1-E79DDC6853EE@lca.pw>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Matthew Wilcox <willy@infradead.org>,
        Mel Gorman <mgorman@suse.de>,
        Kees Cook <keescook@chromium.org>, andi.kleen@intel.com,
        tim.c.chen@intel.com, dave.hansen@intel.com, ying.huang@intel.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Konstantin Khlebnikov <koct9i@gmail.com>
To:     Feng Tang <feng.tang@intel.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On Jun 1, 2020, at 11:37 PM, Feng Tang <feng.tang@intel.com> wrote:
>=20
> I re-run the same benchmark with v5.7 and 5.7+remove_warning kernels,
> the overall performance change is trivial (which is expected)
>=20
>   1330147            +0.1%    1331032        will-it-scale.72.processes
>=20
> But the perf stats of "self" shows big change for __vm_enough_memory()=20
>=20
>      0.27            -0.3        0.00        pp.self.__vm_enough_memory
>=20
> I post the full compare result in the end.

I don=E2=80=99t really see what that means exactly, but I suppose the warnin=
g is there for so long and no one seems notice much trouble (or benefit) bec=
ause of it, so I think you will probably need to come up with a proper justi=
fication to explain why it is a trouble now, and how your patchset suddenly s=
tart to trigger the warning as well as why it is no better way but to suffer=
 this debuggability regression (probably tiny but still).=