linux-kernel - Re: [PATCH v1 12/16] arm64/mm: Support huge pte-mapped pages in vmap

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Message-ID: <72f188c5-c078-4ff5-81a6-3a0c8b2edaea@arm.com>
Date: Mon, 17 Feb 2025 10:03:31 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Ryan Roberts <ryan.roberts@....com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Muchun Song <muchun.song@...ux.dev>,
 Pasha Tatashin <pasha.tatashin@...een.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Uladzislau Rezki <urezki@...il.com>, Christoph Hellwig <hch@...radead.org>,
 Mark Rutland <mark.rutland@....com>, Ard Biesheuvel <ardb@...nel.org>,
 Dev Jain <dev.jain@....com>, Alexandre Ghiti <alexghiti@...osinc.com>,
 Steve Capper <steve.capper@...aro.org>, Kevin Brodsky <kevin.brodsky@....com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 12/16] arm64/mm: Support huge pte-mapped pages in vmap



On 2/13/25 14:39, Ryan Roberts wrote:
> 
>>>>> +#define arch_vmap_pte_range_map_size arch_vmap_pte_range_map_size
>>>>> +static inline unsigned long arch_vmap_pte_range_map_size(unsigned long addr,
>>>>> +						unsigned long end, u64 pfn,
>>>>> +						unsigned int max_page_shift)
>>>>> +{
>>>>> +	if (max_page_shift < CONT_PTE_SHIFT)
>>>>> +		return PAGE_SIZE;
>>>>> +
>>>>> +	if (end - addr < CONT_PTE_SIZE)
>>>>> +		return PAGE_SIZE;
>>>>> +
>>>>> +	if (!IS_ALIGNED(addr, CONT_PTE_SIZE))
>>>>> +		return PAGE_SIZE;
>>>>> +
>>>>> +	if (!IS_ALIGNED(PFN_PHYS(pfn), CONT_PTE_SIZE))
>>>>> +		return PAGE_SIZE;
>>>>> +
>>>>> +	return CONT_PTE_SIZE;
>>>>
>>>> A small nit:
>>>>
>>>> Should the rationale behind picking CONT_PTE_SIZE be added here as an in code
>>>> comment or something in the function - just to make things bit clear.
>>>
>>> I'm not sure what other size we would pick?
>>
>> The suggestion was to add a small comment in the above helper function explaining
>> the rationale for various conditions in there while returning either PAGE_SIZE or
>> CONT_PTE_SIZE to improve readability etc.
> 
> OK I've added the following:
> 
> /*
>  * If the block is at least CONT_PTE_SIZE in size, and is naturally
>  * aligned in both virtual and physical space, then we can pte-map the
>  * block using the PTE_CONT bit for more efficient use of the TLB.
>  */

Sounds good, thanks !