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Date:   Tue, 30 May 2023 10:10:52 +0800
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Subject: Re: [PATCH -next] mm: page_alloc: simplify has_managed_dma()
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To:     Matthew Wilcox <willy@infradead.org>
CC:     Andrew Morton <akpm@linux-foundation.org>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>, Baoquan He <bhe@redhat.com>,
        Mike Rapoport <rppt@kernel.org>
References: <20230529144022.42927-1-wangkefeng.wang@huawei.com>
 <ZHS2AgVvrT3n/hlM@casper.infradead.org>
From:   Kefeng Wang <wangkefeng.wang@huawei.com>
In-Reply-To: <ZHS2AgVvrT3n/hlM@casper.infradead.org>
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On 2023/5/29 22:26, Matthew Wilcox wrote:
> On Mon, May 29, 2023 at 10:40:22PM +0800, Kefeng Wang wrote:
>> The ZONE_DMA should only exists on Node 0, only check NODE_DATA(0)
>> is enough, so simplify has_managed_dma() and make it inline.
> 
> That's true on x86, but is it true on all architectures?

There is no document about numa node info for the DMA_ZONE, + Mike

I used 'git grep -w ZONE_DMA arch/'

1) the following archs without NUMA support, so it's true for them,

arch/alpha/mm/init.c:	max_zone_pfn[ZONE_DMA] = dma_pfn;
arch/arm/mm/init.c:	max_zone_pfn[ZONE_DMA] = min(arm_dma_pfn_limit, 
max_low);
arch/m68k/mm/init.c:	max_zone_pfn[ZONE_DMA] = end_mem >> PAGE_SHIFT;
arch/m68k/mm/mcfmmu.c:	max_zone_pfn[ZONE_DMA] = PFN_DOWN(_ramend);
arch/m68k/mm/motorola.c:	max_zone_pfn[ZONE_DMA] = memblock_end_of_DRAM();
arch/m68k/mm/sun3mmu.c:	max_zone_pfn[ZONE_DMA] = ((unsigned 
long)high_memory) >> PAGE_SHIFT;
arch/microblaze/mm/init.c:	zones_size[ZONE_DMA] = max_low_pfn;
arch/microblaze/mm/init.c:	zones_size[ZONE_DMA] = max_pfn;


2) Simple check following archs, it seems that it is yes to them too.

arch/mips/mm/init.c:	max_zone_pfns[ZONE_DMA] = MAX_DMA_PFN;
arch/powerpc/mm/mem.c:	max_zone_pfns[ZONE_DMA]	= min(max_low_pfn,
arch/s390/mm/init.c:	max_zone_pfns[ZONE_DMA] = PFN_DOWN(MAX_DMA_ADDRESS);
arch/sparc/mm/srmmu.c:		max_zone_pfn[ZONE_DMA] = max_low_pfn;
arch/x86/mm/init.c:	max_zone_pfns[ZONE_DMA]		= min(MAX_DMA_PFN, 
max_low_pfn);
arch/arm64/mm/init.c:	max_zone_pfns[ZONE_DMA] = 
PFN_DOWN(arm64_dma_phys_limit);
arch/loongarch/mm/init.c:	max_zone_pfns[ZONE_DMA] = MAX_DMA_PFN;