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

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Message-ID: <YH10s/7MjxBBsjVL@dhcp22.suse.cz>
Date:   Mon, 19 Apr 2021 14:16:51 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Peter Enderborg <peter.enderborg@...y.com>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Muchun Song <songmuchun@...edance.com>,
        Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>, NeilBrown <neilb@...e.de>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Mike Rapoport <rppt@...nel.org>, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v4] dma-buf: Add DmaBufTotal counter in meminfo

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?
-- 
Michal Hocko
SUSE Labs