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From: Thomas Gleixner <tglx@linutronix.de>
To: Dmitry Safonov <dsafonov@virtuozzo.com>
Cc: linux-kernel@vger.kernel.org, 0x7f454c46@gmail.com,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@suse.de>,
	x86@kernel.org, linux-mm@kvack.org
Subject: Re: [PATCHv4 2/5] x86/mm: introduce mmap{,_legacy}_base
Date: Mon, 13 Feb 2017 16:35:10 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.20.1702131633320.3619@nanos> (raw)
In-Reply-To: <adca283e-3187-dff0-7db6-3cb98d6b3bc5@virtuozzo.com>

On Mon, 13 Feb 2017, Dmitry Safonov wrote:
> 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.

So just leave it alone. 5/6 is pulled from thin air and 128M probably as
well. I hoped there would be some reasonable explanation ....

Thanks,

	tglx

  reply	other threads:[~2017-02-13 15:35 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-01-30 12:04 [PATCHv4 0/5] Fix compatible mmap() return pointer over 4Gb Dmitry Safonov
2017-01-30 12:04 ` [PATCHv4 1/5] x86/mm: split arch_mmap_rnd() on compat/native versions Dmitry Safonov
2017-02-09 13:55   ` Borislav Petkov
2017-02-09 23:06     ` Andy Lutomirski
2017-02-10 20:10     ` Thomas Gleixner
2017-02-10 20:25       ` Borislav Petkov
2017-02-10 21:28       ` Dmitry Safonov
2017-02-11  8:23         ` Thomas Gleixner
2017-02-13 11:12           ` Dmitry Safonov
2017-02-13 11:22             ` Thomas Gleixner
2017-01-30 12:04 ` [PATCHv4 2/5] x86/mm: introduce mmap{,_legacy}_base Dmitry Safonov
2017-02-11 14:13   ` Thomas Gleixner
2017-02-13 13:02     ` Dmitry Safonov
2017-02-13 13:13       ` Thomas Gleixner
2017-02-13 14:37     ` Dmitry Safonov
2017-02-13 15:35       ` Thomas Gleixner [this message]
2017-01-30 12:04 ` [PATCHv4 3/5] x86/mm: fix 32-bit mmap() for 64-bit ELF Dmitry Safonov
2017-02-11 19:49   ` Thomas Gleixner
2017-02-14 15:24     ` Dmitry Safonov
2017-01-30 12:04 ` [PATCHv4 4/5] x86/mm: check in_compat_syscall() instead TIF_ADDR32 for mmap(MAP_32BIT) Dmitry Safonov
2017-02-11 20:13   ` Thomas Gleixner
2017-02-14 16:11     ` Dmitry Safonov
2017-02-14 16:14       ` Dmitry Safonov
2017-01-30 12:04 ` [PATCHv4 5/5] selftests/x86: add test to check compat mmap() return addr Dmitry Safonov
2017-02-06 16:46 ` [PATCHv4 0/5] Fix compatible mmap() return pointer over 4Gb Dmitry Safonov

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