linux-kernel - Re: [PATCH v4] arm64: mm: Populate vmemmap/linear at the page level for hotplugged sections

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Message-ID: <169f8006-ff33-48ca-a680-37fe1cf0efe8@quicinc.com>
Date: Thu, 9 Jan 2025 15:04:48 +0800
From: Zhenhua Huang <quic_zhenhuah@...cinc.com>
To: Anshuman Khandual <anshuman.khandual@....com>,
        Catalin Marinas
	<catalin.marinas@....com>
CC: <will@...nel.org>, <ardb@...nel.org>, <ryan.roberts@....com>,
        <mark.rutland@....com>, <joey.gouly@....com>,
        <dave.hansen@...ux.intel.com>, <akpm@...ux-foundation.org>,
        <chenfeiyang@...ngson.cn>, <chenhuacai@...nel.org>,
        <linux-mm@...ck.org>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <quic_tingweiz@...cinc.com>,
        <stable@...r.kernel.org>
Subject: Re: [PATCH v4] arm64: mm: Populate vmemmap/linear at the page level
 for hotplugged sections



On 2025/1/8 18:11, Anshuman Khandual wrote:
> Just wondering why not start with PUD level itself ? Although SUBSECTION_SHIFT
> might never reach the PUD level but this will help keep the flags calculations
> bit simple and ready for all future changes.
> 

I suppose that it's because these are significantly larger than 2M, 
whereas Catalin assumed SUBSECTION_SIZE would not increase?
His comment:
"should cover any changes to SUBSECTION_SHIFT making it *smaller* than 
2MB. "

> 	flags = 0;
>   	if (SUBSECTION_SHIFT < PUD_SHIFT)
>   		flags |= NO_PUD_BLOCK_MAPPINGS;
>   	if (SUBSECTION_SHIFT < CONT_PMD_SHIFT)
>   		flags |= NO_PMD_CONT_MAPPINGS;