linux-kernel - Re: [PATCHv4 2/5] x86/mm: introduce mmap{,_legacy}

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Message-ID: <adca283e-3187-dff0-7db6-3cb98d6b3bc5@virtuozzo.com>
Date:   Mon, 13 Feb 2017 17:37:09 +0300
From:   Dmitry Safonov <dsafonov@...tuozzo.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     <linux-kernel@...r.kernel.org>, <0x7f454c46@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...e.de>, <x86@...nel.org>,
        <linux-mm@...ck.org>
Subject: Re: [PATCHv4 2/5] x86/mm: introduce mmap{,_legacy}_base

On 02/11/2017 05:13 PM, Thomas Gleixner wrote:
>> -static unsigned long mmap_base(unsigned long rnd)
>> +static unsigned long mmap_base(unsigned long rnd, unsigned long task_size)
>>  {
>> 	unsigned long gap = rlimit(RLIMIT_STACK);
> 	unsigned long gap_min, gap_max;
>
> 	/* Add comment what this means */
> 	gap_min = SIZE_128M + stack_maxrandom_size(task_size);
> 	/* Explain that ' /6 * 5' magic */
> 	gap_max = (task_size / 6) * 5;

So, I can't find about those limits on a gap size:
They were introduced by commit 8913d55b6c58 ("i386 virtual memory
layout rework").
All I could find is that 128Mb limit was more limit on virtual adress
space than on a memory available those days.
And 5/6 of task_size looks like heuristic value.
So I'm not sure, what to write in comments:
that rlimit on stack can't be bigger than 5/6 of task_size?
That looks obvious from the code.

-- 
              Dmitry