linux-kernel - Re: [PACTH v2 0/3] Implement /proc/<pid>/totmaps

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Date:   Tue, 30 Aug 2016 10:15:34 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Sonny Rao <sonnyrao@...omium.org>
Cc:     Jann Horn <jann@...jh.net>,
        Robert Foss <robert.foss@...labora.com>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Konstantin Khlebnikov <koct9i@...il.com>,
        Hugh Dickins <hughd@...gle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Minchan Kim <minchan@...nel.org>,
        John Stultz <john.stultz@...aro.org>,
        ross.zwisler@...ux.intel.com, jmarchan@...hat.com,
        Johannes Weiner <hannes@...xchg.org>,
        Kees Cook <keescook@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Robin Humble <plaguedbypenguins@...il.com>,
        David Rientjes <rientjes@...gle.com>,
        eric.engestrom@...tec.com, Janis Danisevskis <jdanis@...gle.com>,
        calvinowens@...com, Alexey Dobriyan <adobriyan@...il.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        ldufour@...ux.vnet.ibm.com, linux-doc@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ben Zhang <benzh@...omium.org>,
        Bryan Freed <bfreed@...omium.org>,
        Filipe Brandenburger <filbranden@...omium.org>,
        Mateusz Guzik <mguzik@...hat.com>
Subject: Re: [PACTH v2 0/3] Implement /proc/<pid>/totmaps

On Mon 29-08-16 16:37:04, Michal Hocko wrote:
> [Sorry for a late reply, I was busy with other stuff]
> 
> On Mon 22-08-16 15:44:53, Sonny Rao wrote:
> > On Mon, Aug 22, 2016 at 12:54 AM, Michal Hocko <mhocko@...nel.org> wrote:
> [...]
> > But what about the private_clean and private_dirty?  Surely
> > those are more generally useful for calculating a lower bound on
> > process memory usage without additional knowledge?
> 
> I guess private_clean can be used as a reasonable estimate.

I was thinking about this more and I think I am wrong here. Even truly
MAP_PRIVATE|MAP_ANON will be in private_dirty. So private_clean will
become not all that interesting and similarly misleading as its _dirty
variant (mmaped file after [m]sync should become _clean) and that
doesn't mean the memory will get freed after the process which maps it
terminates. Take shmem as an example again.

> private_dirty less so because it may refer to e.g. tmpfs which is not
> mapped by other process and so no memory would be freed after unmap
> without removing the file.

-- 
Michal Hocko
SUSE Labs