linux-kernel - Re: [PATCH 0/3] mm/mmap.c: don't unmap the overlapping VMA(s)

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Date:	Mon, 4 Apr 2016 17:26:43 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Michal Hocko <mhocko@...nel.org>,
	Piotr Kwapulinski <kwapulinski.piotr@...il.com>
Cc:	akpm@...ux-foundation.org, mtk.manpages@...il.com,
	cmetcalf@...lanox.com, arnd@...db.de, viro@...iv.linux.org.uk,
	mszeredi@...e.cz, dave@...olabs.net,
	kirill.shutemov@...ux.intel.com, mingo@...nel.org,
	dan.j.williams@...el.com, dave.hansen@...ux.intel.com,
	koct9i@...il.com, hannes@...xchg.org, jack@...e.cz,
	xiexiuqi@...wei.com, iamjoonsoo.kim@....com, oleg@...hat.com,
	gang.chen.5i5j@...il.com, aarcange@...hat.com,
	aryabinin@...tuozzo.com, rientjes@...gle.com, denc716@...il.com,
	toshi.kani@....com, ldufour@...ux.vnet.ibm.com,
	kuleshovmail@...il.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 0/3] mm/mmap.c: don't unmap the overlapping VMA(s)

On 04/04/2016 09:31 AM, Michal Hocko wrote:
> On Sat 02-04-16 21:17:31, Piotr Kwapulinski wrote:
>> Currently the mmap(MAP_FIXED) discards the overlapping part of the
>> existing VMA(s).
>> Introduce the new MAP_DONTUNMAP flag which forces the mmap to fail
>> with ENOMEM whenever the overlapping occurs and MAP_FIXED is set.
>> No existing mapping(s) is discarded.
>
> You forgot to tell us what is the use case for this new flag.

Exactly. Also, returning ENOMEM is strange, EINVAL might be a better 
match, otherwise how would you distinguish a "geunine" ENOMEM from 
passing a wrong address?