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Date: Sat, 11 Feb 2012 15:49:01 +0530
Message-ID: <CAAHN_R1=87w+NFXPA5MGER8wLR4LwOv-2_eG-d+Fe=+j08FKYQ@mail.gmail.com>
Subject: Re: [RESEND][PATCH] Mark thread stack correctly in proc/<pid>/maps
From: Siddhesh Poyarekar <siddhesh.poyarekar@gmail.com>
To: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: Jamie Lokier <jamie@shareable.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org,
        Michael Kerrisk <mtk.manpages@gmail.com>, linux-man@vger.kernel.org,
        Mike Frysinger <vapier@gentoo.org>
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On Wed, Feb 8, 2012 at 11:27 PM, KOSAKI Motohiro
<kosaki.motohiro@gmail.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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