linux-kernel - Re: [PATCH] proc: revert /proc/<pid>/maps [stack:TID] annotation

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Message-ID: <CAAHN_R2CFYsSSU_Qr-_cE+9-=OqDOa88annh9uA1TymuJncL8A@mail.gmail.com>
Date:	Wed, 20 Jan 2016 08:47:39 +0530
From:	Siddhesh Poyarekar <siddhesh.poyarekar@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Johannes Weiner <hannes@...xchg.org>, Shaohua Li <shli@...com>,
	linux-mm@...ck.org, linux-kernel <linux-kernel@...r.kernel.org>,
	kernel-team@...com
Subject: Re: [PATCH] proc: revert /proc/<pid>/maps [stack:TID] annotation

On 20 January 2016 at 03:44, Andrew Morton <akpm@...ux-foundation.org> wrote:
> Any thoughts on the obvious back-compatibility concerns?  ie, why did
> Siddhesh implement this in the first place?  My bad for not ensuring
> that the changelog told us this.
>
> https://lkml.org/lkml/2012/1/14/25 has more info:
>
> : Memory mmaped by glibc for a thread stack currently shows up as a
> : simple anonymous map, which makes it difficult to differentiate between
> : memory usage of the thread on stack and other dynamic allocation.
> : Since glibc already uses MAP_STACK to request this mapping, the
> : attached patch uses this flag to add additional VM_STACK_FLAGS to the
> : resulting vma so that the mapping is treated as a stack and not any
> : regular anonymous mapping.  Also, one may use vm_flags to decide if a
> : vma is a stack.
>
> But even that doesn't really tell us what the actual *value* of the
> patch is to end-users.

The end users needed a way to identify thread stacks programmatically
and there wasn't a way to do that.  I'm afraid I no longer remember
(or have access to the resources that would aid my memory since I
changed employers) the details of their requirement.  However, I did
do this on my own time because I thought it was an interesting project
for me and nobody really gave any feedback then as to its utility, so
as far as I am concerned you could roll back the main thread maps
information since the information is available in the thread-specific
files.

Siddhesh
-- 
http://siddhesh.in