Re: [PATCH v2] arm64: mm: reserve hugetlb CMA after numa_init

On Wed, Jun 17, 2020 at 09:43:51PM +0000, Song Bao Hua (Barry Song) wrote:

quoted

From: Roman Gushchin [mailto:guro@fb.com]
On Wed, Jun 17, 2020 at 11:38:03AM +0000, Song Bao Hua (Barry Song)

quoted

quoted

From: Will Deacon [mailto:will@kernel.org]
On Wed, Jun 17, 2020 at 10:19:24AM +1200, Barry Song wrote:

quoted

hugetlb_cma_reserve() is called at the wrong place. numa_init has not

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index e631e6425165..41914b483d54 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c

@@ -404,11 +404,6 @@ void __init arm64_memblock_init(void)
 	high_memory = __va(memblock_end_of_DRAM() - 1) + 1;

 	dma_contiguous_reserve(arm64_dma32_phys_limit);
-
-#ifdef CONFIG_ARM64_4K_PAGES
-	hugetlb_cma_reserve(PUD_SHIFT - PAGE_SHIFT);
-#endif

Why is this dependent on CONFIG_ARM64_4K_PAGES? We unconditionally
select ARCH_HAS_GIGANTIC_PAGE so this seems unnecessary.

Roman, would you like to answer this question? Have you found any

problem if system

quoted

doesn't set 4K_PAGES?

No, I was just following the code in arch/arm64/mm/hugetlbpage.c where all
related to PUD-sized pages is guarded by CONFIG_ARM64_4K_PAGES.
Actually I did all my testing on x86-64, I don't even have any arm hardware.

I'm totally fine with removing this #ifdef if it's not needed.

At this moment, I would suggest we should keep this "ifdef". Otherwise, hugetlb_cma_reserve() won't be really useful.

For example, while setting PAGE size to 64KB. I got this error in hugetlb_cma_reserve():
hugetlb_cma: cma area should be at least 4194304 MiB
This is absolutely unreasonable.

Maybe one for RaspberryPi 5, huh? ;)

But ok, I'll take your patch as-is and add a comment about NUMA.

Thanks,

Will

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