linux-kernel - Re: [PATCH v4] dma-buf: Add DmaBufTotal counter in meminfo

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Message-ID: <c3f0da9c-d127-5edf-dd21-50fd5298acef@sony.com>
Date:   Mon, 19 Apr 2021 12:41:58 +0000
From:   <Peter.Enderborg@...y.com>
To:     <mhocko@...e.com>
CC:     <linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <sumit.semwal@...aro.org>, <christian.koenig@....com>,
        <adobriyan@...il.com>, <akpm@...ux-foundation.org>,
        <songmuchun@...edance.com>, <guro@...com>, <shakeelb@...gle.com>,
        <neilb@...e.de>, <samitolvanen@...gle.com>, <rppt@...nel.org>,
        <linux-media@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <linaro-mm-sig@...ts.linaro.org>, <willy@...radead.org>
Subject: Re: [PATCH v4] dma-buf: Add DmaBufTotal counter in meminfo

On 4/19/21 2:16 PM, Michal Hocko wrote:
> On Sat 17-04-21 12:40:32, Peter Enderborg wrote:
>> This adds a total used dma-buf memory. Details
>> can be found in debugfs, however it is not for everyone
>> and not always available. dma-buf are indirect allocated by
>> userspace. So with this value we can monitor and detect
>> userspace applications that have problems.
> The changelog would benefit from more background on why this is needed,
> and who is the primary consumer of that value.
>
> I cannot really comment on the dma-buf internals but I have two remarks.
> Documentation/filesystems/proc.rst needs an update with the counter
> explanation and secondly is this information useful for OOM situations
> analysis? If yes then show_mem should dump the value as well.
>
> From the implementation point of view, is there any reason why this
> hasn't used the existing global_node_page_state infrastructure?

I fix doc in next version.  Im not sure what you expect the commit message to include.

The function of the meminfo is: (From Documentation/filesystems/proc.rst)

"Provides information about distribution and utilization of memory."

Im not the designed of dma-buf, I think  global_node_page_state as a kernel
internal. dma-buf is a device driver that provides a function so I might be
on the outside. However I also see that it might be relevant for a OOM.
It is memory that can be freed by killing userspace processes.

The show_mem thing. Should it be a separate patch?