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Date:   Mon, 7 Sep 2020 10:05:11 +0300
From:   Mike Rapoport <rppt@linux.ibm.com>
To:     Randy Dunlap <rdunlap@infradead.org>
Cc:     LKML <linux-kernel@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Nazarewicz <mina86@mina86.com>,
        Wen Congyang <wency@cn.fujitsu.com>,
        Michal Simek <monstr@monstr.eu>,
        Christoph Hellwig <hch@lst.de>,
        kernel test robot <lkp@intel.com>
Subject: Re: [PATCH] <linux/page-isolation.h>: provide stubs for
 MEMORY_ISOLATION not set (for Microblaze)
Message-ID: <20200907070511.GN424181@linux.ibm.com>
References: <1f6b42e6-b6b5-40e3-92b4-77bd610d3e49@infradead.org>
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Hi Randy,

On Sun, Sep 06, 2020 at 12:33:08PM -0700, Randy Dunlap wrote:
> From: Randy Dunlap <rdunlap@infradead.org>
> 
> Fix build errors in Microblaze when CONFIG_MEMORY_ISOLATION is not
> set/enabled by adding stubs for 3 missing functions.

I've tried to follow Kconfig dependencies to see how could we have both
CONTIG_ALLOC=y and CONFIG_MEMORY_ISOLATION=n and I could not find how
was this possible.

We have 

config CONTIG_ALLOC
	def_bool (MEMORY_ISOLATION && COMPACTION) || CMA

and

config CMA
	bool "Contiguous Memory Allocator"
	depends on MMU
	select MIGRATION
	select MEMORY_ISOLATION

and alloc_contig_range() is hidden behind '#ifdef CONFIG_CONTIG_ALLOC'

In any rate, I think the better fix would be to update Kconfig
dependencies rather than add stubs for these functions.

> Fixes these build errors:
> 
> gcc-9.3.0-nolibc/microblaze-linux/bin/microblaze-linux-ld: mm/page_alloc.o: in function `alloc_contig_range':
> (.text+0xa0c0): undefined reference to `start_isolate_page_range'
> gcc-9.3.0-nolibc/microblaze-linux/bin/microblaze-linux-ld: (.text+0xa2bc): undefined reference to `test_pages_isolated'
> gcc-9.3.0-nolibc/microblaze-linux/bin/microblaze-linux-ld: (.text+0xa378): undefined reference to `undo_isolate_page_range'
> 
> Fixes: 0815f3d81d76 ("mm: page_isolation: MIGRATE_CMA isolation functions added") # v3.10
> Fixes: b023f46813cd ("memory-hotplug: skip HWPoisoned page when offlining pages") # v3.10
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
> Cc: Michal Nazarewicz <mina86@mina86.com>
> Cc: Wen Congyang <wency@cn.fujitsu.com>
> Cc: Michal Simek <monstr@monstr.eu>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Mike Rapoport <rppt@linux.ibm.com>
> Cc: linux-mm@kvack.org
> ---
>  include/linux/page-isolation.h |   16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> --- linux-next-20200903.orig/include/linux/page-isolation.h
> +++ linux-next-20200903/include/linux/page-isolation.h
> @@ -28,6 +28,22 @@ static inline bool is_migrate_isolate(in
>  {
>  	return false;
>  }
> +static inline int test_pages_isolated(unsigned long start_pfn,
> +				      unsigned long end_pfn, int isol_flags)
> +{
> +	return 0;
> +}
> +static inline int
> +start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> +			 unsigned migratetype, int flags)
> +{
> +	return 0;
> +}
> +static inline void
> +undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> +			unsigned migratetype)
> +{
> +}
>  #endif
>  
>  #define MEMORY_OFFLINE	0x1
> 
> 

-- 
Sincerely yours,
Mike.