linux-kernel - Re: [RFC PATCH 2/7] mm: vmalloc: don't account for number of nodes for HUGE

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Message-ID: <9217c95a-39f6-49ce-9857-ee2eebdb7a16@csgroup.eu>
Date: Fri, 12 Apr 2024 06:07:19 +0000
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Mike Rapoport <rppt@...nel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: Andrew Morton <akpm@...ux-foundation.org>, Andy Lutomirski
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	Uladzislau Rezki <urezki@...il.com>, Will Deacon <will@...nel.org>,
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Subject: Re: [RFC PATCH 2/7] mm: vmalloc: don't account for number of nodes
 for HUGE_VMAP allocations



Le 11/04/2024 à 18:05, Mike Rapoport a écrit :
> From: "Mike Rapoport (IBM)" <rppt@...nel.org>
> 
> vmalloc allocations with VM_ALLOW_HUGE_VMAP that do not explictly
> specify node ID will use huge pages only if size_per_node is larger than
> PMD_SIZE.
> Still the actual allocated memory is not distributed between nodes and
> there is no advantage in such approach.
> On the contrary, BPF allocates PMD_SIZE * num_possible_nodes() for each
> new bpf_prog_pack, while it could do with PMD_SIZE'ed packs.
> 
> Don't account for number of nodes for VM_ALLOW_HUGE_VMAP with
> NUMA_NO_NODE and use huge pages whenever the requested allocation size
> is larger than PMD_SIZE.

Patch looks ok but message is confusing. We also use huge pages at PTE 
size, for instance 512k pages or 16k pages on powerpc 8xx, while 
PMD_SIZE is 4M.

Christophe

> 
> Signed-off-by: Mike Rapoport (IBM) <rppt@...nel.org>
> ---
>   mm/vmalloc.c | 9 ++-------
>   1 file changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 22aa63f4ef63..5fc8b514e457 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3737,8 +3737,6 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
>   	}
>   
>   	if (vmap_allow_huge && (vm_flags & VM_ALLOW_HUGE_VMAP)) {
> -		unsigned long size_per_node;
> -
>   		/*
>   		 * Try huge pages. Only try for PAGE_KERNEL allocations,
>   		 * others like modules don't yet expect huge pages in
> @@ -3746,13 +3744,10 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
>   		 * supporting them.
>   		 */
>   
> -		size_per_node = size;
> -		if (node == NUMA_NO_NODE)
> -			size_per_node /= num_online_nodes();
> -		if (arch_vmap_pmd_supported(prot) && size_per_node >= PMD_SIZE)
> +		if (arch_vmap_pmd_supported(prot) && size >= PMD_SIZE)
>   			shift = PMD_SHIFT;
>   		else
> -			shift = arch_vmap_pte_supported_shift(size_per_node);
> +			shift = arch_vmap_pte_supported_shift(size);
>   
>   		align = max(real_align, 1UL << shift);
>   		size = ALIGN(real_size, 1UL << shift);