linux-kernel - Re: [RFC] fs/proc/meminfo: introduce Unaccounted statistic

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Date:   Fri, 21 Oct 2016 09:31:44 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Johannes Weiner <hannes@...xchg.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Hugh Dickins <hughd@...gle.com>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [RFC] fs/proc/meminfo: introduce Unaccounted statistic

On 10/20/2016 03:33 PM, Michal Hocko wrote:
> On Thu 20-10-16 14:11:49, Vlastimil Babka wrote:
> [...]
>> Hi, I'm wondering if people would find this useful. If you think it is, and
>> to not make performance worse, I could also make sure in proper submission
>> that values are not read via global_page_state() multiple times etc...
>
> I definitely find this information useful and hate to do the math all
> the time but on the other hand this is quite fragile and I can imagine
> we can easily forget to add something there and provide a misleading
> information to the userspace. So I would be worried with a long term
> maintainability of this.

I wouldn't fear this that much. Maybe even on the contrary - if we unknowingly 
change the picture by misacounting something, or changing a counter to become 
subset of another, and Unaccounted starts to give weird values, it will give us 
hint that there's either a problem to fix, or a missed documentation update.