linux-kernel - Re: [PATCH v4 3/4] mm/util.c: remove the VM_WARN_ONCE for vm_committed

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Message-Id: <E1703973-38C1-4AFB-94D1-E79DDC6853EE@lca.pw>
Date:   Tue, 2 Jun 2020 00:02:22 -0400
From:   Qian Cai <cai@....pw>
To:     Feng Tang <feng.tang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...e.de>,
        Kees Cook <keescook@...omium.org>, andi.kleen@...el.com,
        tim.c.chen@...el.com, dave.hansen@...el.com, ying.huang@...el.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Konstantin Khlebnikov <koct9i@...il.com>
Subject: Re: [PATCH v4 3/4] mm/util.c: remove the VM_WARN_ONCE for vm_committed_as underflow check



> On Jun 1, 2020, at 11:37 PM, Feng Tang <feng.tang@...el.com> wrote:
> 
> I re-run the same benchmark with v5.7 and 5.7+remove_warning kernels,
> the overall performance change is trivial (which is expected)
> 
>   1330147            +0.1%    1331032        will-it-scale.72.processes
> 
> But the perf stats of "self" shows big change for __vm_enough_memory() 
> 
>      0.27            -0.3        0.00        pp.self.__vm_enough_memory
> 
> I post the full compare result in the end.

I don’t really see what that means exactly, but I suppose the warning is there for so long and no one seems notice much trouble (or benefit) because of it, so I think you will probably need to come up with a proper justification to explain why it is a trouble now, and how your patchset suddenly start to trigger the warning as well as why it is no better way but to suffer this debuggability regression (probably tiny but still).