Date: Tue, 14 Apr 2015 12:38:53 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Pavel Emelyanov <xemul@parallels.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Hugh Dickins <hughd@google.com>, Rik van Riel <riel@redhat.com>,
        Mel Gorman <mgorman@suse.de>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>, linuxppc-dev@lists.ozlabs.org,
        cov@codeaurora.org, criu@openvz.org
Subject: Re: [RESEND PATCH v3 1/2] mm: Introducing arch_remap hook
Message-Id: <20150414123853.a3e61b7fa95b6c634e0fcce0@linux-foundation.org>
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On Tue, 14 Apr 2015 11:26:13 +0200 Laurent Dufour <ldufour@linux.vnet.ibm.com> wrote:

> > Do away with __HAVE_ARCH_REMAP and do it like this:
> > 
> > arch/x/include/asm/y.h:
> > 
> > 	extern void arch_remap(...);
> > 	#define arch_remap arch_remap
> > 
> > include/linux/z.h:
> > 
> > 	#include <asm/y.h>
> > 
> > 	#ifndef arch_remap
> > 	static inline void arch_remap(...) { }
> > 	#define arch_remap arch_remap
> > 	#endif
> 
> Hi Andrew,
> 
> I like your idea, but I can't find any good candidate for <asm/y.h> and
> <linux/z.h>.
> 
> I tried with <linux/mm.h> and <asm/mmu_context.h> but
> <asm/mmu_context.h> is already including <linux/mm.h>.
> 
> Do you have any suggestion ?
> 
> Another option could be to do it like the actual arch_unmap() in
> <asm-generic/mm_hooks.h> but this is the opposite of your idea, and Ingo
> was not comfortable with this idea due to the impact of the other
> architectures.

I don't see any appropriate header files for this.  mman.h is kinda
close.

So we create new header files, that's not a problem.  I'm torn between

a) include/linux/mm-arch-hooks.h (and 31
   arch/X/include/asm/mm-arch-hooks.h).  Mandate: mm stuff which can be
   overridded by arch

versus

b) include/linux/mremap.h (+31), with a narrower mandate.


This comes up fairly regularly so I suspect a) is better.  We'll add
things to it over time, and various bits of existing ad-hackery can be
moved over as cleanups.

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