linux-kernel - Re: [PATCH] proc/meminfo: add MemKernel counter

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Message-ID: <177f56cd-6e10-4d2e-7a3e-23276222ba19@yandex-team.ru>
Date:   Wed, 22 May 2019 19:09:22 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Roman Gushchin <guro@...com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH] proc/meminfo: add MemKernel counter

On 22.05.2019 18:52, Michal Hocko wrote:
> On Wed 22-05-19 17:40:09, Konstantin Khlebnikov wrote:
>> Some kinds of kernel allocations are not accounted or not show in meminfo.
>> For example vmalloc allocations are tracked but overall size is not shown
>> for performance reasons. There is no information about network buffers.
>>
>> In most cases detailed statistics is not required. At first place we need
>> information about overall kernel memory usage regardless of its structure.
>>
>> This patch estimates kernel memory usage by subtracting known sizes of
>> free, anonymous, hugetlb and caches from total memory size: MemKernel =
>> MemTotal - MemFree - Buffers - Cached - SwapCached - AnonPages - Hugetlb.
> 
> Why do we need to export something that can be calculated in the
> userspace trivially? Also is this really something the number really
> meaningful? Say you have a driver that exports memory to the userspace
> via mmap but that memory is not accounted. Is this really a kernel
> memory?
> 

It may be trivial right now but not fixed.
Adding new kinds of memory may change this definition.
For example hypothetical 'GPU buffers' may be handled as 'userspace' memory.