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

-----Original Message-----
From: Roman Gushchin [mailto:guro@fb.com]
Sent: Thursday, June 18, 2020 6:20 AM
To: Song Bao Hua (Barry Song) <redacted>
Cc: Will Deacon <will@kernel.org>; catalin.marinas@arm.com;
nsaenzjulienne@suse.de; steve.capper@arm.com; rppt@linux.ibm.com;
akpm@linux-foundation.org; linux-arm-kernel@lists.infradead.org;
linux-kernel@vger.kernel.org; Linuxarm [off-list ref]; Matthias
Brugger [off-list ref]
Subject: Re: [PATCH v2] arm64: mm: reserve hugetlb CMA after numa_init

On Wed, Jun 17, 2020 at 11:38:03AM +0000, Song Bao Hua (Barry Song)
wrote:

quoted

quoted

-----Original Message-----
From: Will Deacon [mailto:will@kernel.org]
Sent: Wednesday, June 17, 2020 10:18 PM
To: Song Bao Hua (Barry Song) <redacted>
Cc: catalin.marinas@arm.com; nsaenzjulienne@suse.de;
steve.capper@arm.com; rppt@linux.ibm.com;

akpm@linux-foundation.org;

quoted

quoted

linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;

Linuxarm

quoted

quoted

[off-list ref]; Matthias Brugger [off-list ref];
Roman Gushchin [off-list ref]
Subject: Re: [PATCH v2] arm64: mm: reserve hugetlb CMA after numa_init

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

been

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done yet. so all reserved memory will be located at node0.

Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic

hugepages

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using cma")

Damn, wasn't CC'd on that :/

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Cc: Matthias Brugger <matthias.bgg@gmail.com>
Acked-by: Roman Gushchin <redacted>
Signed-off-by: Barry Song <redacted>
---
 -v2: add Fixes tag according to Matthias Brugger's comment

 arch/arm64/mm/init.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

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.

Supporting hugetlb_cma_reserve() for page sizes other than 4k is a different issue. 
It might be addressed in a separate patch later.

Thanks!

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-
 }

 void __init bootmem_init(void)

@@ -424,6 +419,11 @@ void __init bootmem_init(void)
 	min_low_pfn = min;

 	arm64_numa_init();
+
+#ifdef CONFIG_ARM64_4K_PAGES
+	hugetlb_cma_reserve(PUD_SHIFT - PAGE_SHIFT);
+#endif

A comment here wouldn't hurt, as it does look a lot more natural next
to dma_contiguous_reserve().

Will add some comment here.

quoted

Will

barry

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