linux-kernel - Re: [RESEND][PATCH] Mark thread stack correctly in proc/<pid>/maps

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Date:	Sat, 11 Feb 2012 15:49:01 +0530
From:	Siddhesh Poyarekar <siddhesh.poyarekar@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	Jamie Lokier <jamie@...reable.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org,
	Michael Kerrisk <mtk.manpages@...il.com>,
	linux-man@...r.kernel.org, Mike Frysinger <vapier@...too.org>
Subject: Re: [RESEND][PATCH] Mark thread stack correctly in proc/<pid>/maps

On Wed, Feb 8, 2012 at 11:27 PM, KOSAKI Motohiro
<kosaki.motohiro@...il.com> wrote:
> Now, we are using some bit saving hack. example,
>
> 1) use ifdef
>
> #ifndef CONFIG_TRANSPARENT_HUGEPAGE
> #define VM_MAPPED_COPY 0x01000000      /* T if mapped copy of data (nommu
> mmap) */
> #else
> #define VM_HUGEPAGE    0x01000000      /* MADV_HUGEPAGE marked this vma */
> #endif
>
> 2) use bit combination
>
> #define VM_STACK_INCOMPLETE_SETUP      (VM_RAND_READ | VM_SEQ_READ)
>
>
> Maybe you can take a similar way. And of course, you can ban some useless
> flag
> bits.

I found the thread in which Linus rejected the idea of expanding vm_flags:

https://lkml.org/lkml/2011/11/10/522

and based on that, I don't think I can justify the need for a new flag
for this patch since it is purely for display purposes and has nothing
to do with the actual treatment of the vma. So I figured out another
way to identify a thread stack without changing the way the vma
properties (I should have done this in the first place I think) which
is by checking if the vma contains the stack pointer of the task.

With this change:

/proc/pid/task/tid/maps: will only mark the stack that the task uses

/proc/pid/maps: will mark all stacks. This path will be slower since
it will iterate through the entire thread group for each vma.

I'll test this and attach a new version of the patch.

Regards,
Siddhesh

-- 
Siddhesh Poyarekar
http://siddhesh.in
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