linux-kernel - Re: [PATCH v6 02/10] x86, mpx: add MPX specific mmap interface

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Message-ID: <CALCETrXYZZiZsDiUvvZd0636+qHP9a0sHTN6wt_ZKjvLaeeBzw@mail.gmail.com>
Date:	Mon, 23 Jun 2014 13:06:37 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Dave Hansen <dave.hansen@...el.com>
Cc:	Qiaowei Ren <qiaowei.ren@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>
Subject: Re: [PATCH v6 02/10] x86, mpx: add MPX specific mmap interface

On Mon, Jun 23, 2014 at 1:03 PM, Dave Hansen <dave.hansen@...el.com> wrote:
> On 06/23/2014 12:49 PM, Andy Lutomirski wrote:
>> On 06/18/2014 02:44 AM, Qiaowei Ren wrote:
>>> This patch adds one MPX specific mmap interface, which only handles
>>> mpx related maps, including bounds table and bounds directory.
>>>
>>> In order to track MPX specific memory usage, this interface is added
>>> to stick new vm_flag VM_MPX in the vma_area_struct when create a
>>> bounds table or bounds directory.
>>
>> I imagine the linux-mm people would want to think about any new vm flag.
>>  Why is this needed?
>
> These tables can take huge amounts of memory.  In the worst-case
> scenario, the tables can be 4x the size of the data structure being
> tracked.  IOW, a 1-page structure can require 4 bounds-table pages.
>
> My expectation is that folks using MPX are going to be keen on figuring
> out how much memory is being dedicated to it.  With this feature, plus
> some grepping in /proc/$pid/smaps one could take a pretty good stab at it.
>
> I know VM flags are scarce, and I'm open to other ways to skin this cat.
>

Can the new vm_operation "name" be use for this?  The magic "always
written to core dumps" feature might need to be reconsidered.

There's also arch_vma_name, but I just finished removing for x86, and
I'd be a little sad to see it come right back.

--Andy
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