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Subject: Re: [PATCH 0/2] mm: introduce MAP_FIXED_SAFE
References: <20171129144219.22867-1-mhocko@kernel.org>
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 <20171206045433.GQ26021@bombadil.infradead.org>
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 <5f4fc834-274a-b8f1-bda0-5bcddc5902ed@nvidia.com>
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From: Florian Weimer <fweimer@redhat.com>
Message-ID: <66677640-5c4a-0758-9560-e45de2d5ba06@redhat.com>
Date: Wed, 6 Dec 2017 09:54:30 +0100
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To: John Hubbard <jhubbard@nvidia.com>, Matthew Wilcox <willy@infradead.org>, Michael Ellerman <mpe@ellerman.id.au>
Cc: Cyril Hrubis <chrubis@suse.cz>, Michal Hocko <mhocko@kernel.org>, Kees Cook <keescook@chromium.org>, Linux API <linux-api@vger.kernel.org>, Khalid Aziz <khalid.aziz@oracle.com>, Andrew Morton <akpm@linux-foundation.org>, Russell King - ARM Linux <linux@armlinux.org.uk>, Andrea Arcangeli <aarcange@redhat.com>, Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>, linux-arch <linux-arch@vger.kernel.org>, Abdul Haleem <abdhalee@linux.vnet.ibm.com>, Joel Stanley <joel@jms.id.au>

On 12/06/2017 09:06 AM, John Hubbard wrote:
> On 12/05/2017 11:35 PM, Florian Weimer wrote:
>> On 12/06/2017 08:33 AM, John Hubbard wrote:
>>> In that case, maybe:
>>>
>>>  A A A A  MAP_EXACT
>>>
>>> ? ...because that's the characteristic behavior.
>>
>> Is that true?A  mmap still silently rounding up the length to the page size, I assume, so even that name is misleading.
> 
> Hi Florian,
> 
> Not as far as I can tell, it's not doing that.
> 
> For both MAP_FIXED, and this new flag, the documented (and actual)
> behavior is *not* to do any such rounding. Instead, the requested
> input address is required to be page-aligned itself, and mmap()
> should be honoring the exact addr.

I meant the length, not the address.

Florian

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