linux-kernel - Re: Using remap_pfn_range() to increase total_vm beyond RLIMIT

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Message-ID: <4ADBCCFA.1020507@goop.org>
Date:	Mon, 19 Oct 2009 11:20:42 +0900
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Earl Chew <earl_chew@...lent.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Using remap_pfn_range() to increase total_vm beyond RLIMIT_AS

On 10/16/09 06:17, Earl Chew wrote:
> remap_pfn_range() is defined in mm/memory.c and as far as I
> can tell, does _not_ cause total_vm or reserved_vm to be updated.
>
> Is this right?
>
>
> RLIMIT_AS is only checked against total_vm in mm/mmap.c in the function
> may_expand_vm().
>
> I think this means that a device driver can map pages into
> a process and thus effectively increase address space of
> a process above and beyond the limit set by RLIMIT_AS.

I suspect this is justified because remap_pfn_range is generally
(always?) used to map device memory, and other memory which isn't
represented by struct pages, so it doesn't really count as real memory
usage.

    J
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