linux-kernel - Re: [REGRESSION] "Locked" and "Pss" in /proc/*/smaps are the same

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Date:   Wed, 4 Jul 2018 10:46:52 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Daniel Colascione <dancol@...gle.com>
Cc:     Thomas Lindroth <thomas.lindroth@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm <linux-mm@...ck.org>
Subject: Re: [REGRESSION] "Locked" and "Pss" in /proc/*/smaps are the same

On 07/03/2018 06:20 PM, Daniel Colascione wrote:
> On Tue, Jul 3, 2018 at 12:36 AM, Vlastimil Babka <vbabka@...e.cz> wrote:
>> +CC
>>
>> On 07/01/2018 08:31 PM, Thomas Lindroth wrote:
>>> While looking around in /proc on my v4.14.52 system I noticed that
>>> all processes got a lot of "Locked" memory in /proc/*/smaps. A lot
>>> more memory than a regular user can usually lock with mlock().
>>>
>>> commit 493b0e9d945fa9dfe96be93ae41b4ca4b6fdb317 (v4.14-rc1) seems
>>> to have changed the behavior of "Locked".
> 
> Thanks for fixing that. I submitted a patch [1] for this bug and some
> others a while ago, but the patch didn't make it into the tree because
> or wasn't split up correctly or something, and I had to do other work.

Hmm I see. I pondered about the patch and wondered if the scenarios it
fixes are really possible for smaps_rollup. Did you observe them in
practice? Namely:
- when seq_file starts and stops multiple times on a single open file
description
- when it issues multiple show calls for the same iterator value

I don't think it can happen when all positions but the last one just
return SEQ_SKIP.

Anyway I think the seq_file iterator API usage for smaps_rollup is
unnecessary. Semantically the file shows only one "element" and that's
the set of rollup values for all vmas. Letting seq_file do the iteration
over vmas brings only complications?

> [1] https://marc.info/?l=linux-mm&m=151927723128134&w=2
>