linux-kernel - Re: Re: [PATCH 0/1] arm64/sparsemem: reduce SECTION_SIZE

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Date:   Thu, 28 Jan 2021 19:17:40 -0500
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-kernel@...r.kernel.org,
        Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Sudarshan Rajagopalan <sudaraja@...eaurora.org>,
        David Hildenbrand <david@...hat.com>, linux-mm@...ck.org
Cc:     kernel-team@...roid.com
Subject: Re: Re: [PATCH 0/1] arm64/sparsemem: reduce SECTION_SIZE_BITS



On 1/21/21 1:26 PM, Will Deacon wrote:
> On Wed, 20 Jan 2021 21:29:12 -0800, Sudarshan Rajagopalan wrote:
>> This patch is the follow-up from the discussions in the thread [1].
>> Reducing the section size has the merit of reducing wastage of reserved memory
>> for vmmemmap mappings for sections with large memory holes. Also with smaller
>> section size gives more grunularity and agility for memory hot(un)plugging.
>>
>> But there are also constraints in reducing SECTION_SIZE_BIT:
>>
>> [...]
> 
> Applied to arm64 (for-next/misc), thanks!

We have been using 128M for 4K pages for a while, using patch [1] without issues.

One thing that needs to be also modified is makedumpfile [2]- line 76, must update it SECTIONS_SIZE_BITS based on the PAGESIZE.

[1] https://lore.kernel.org/lkml/20190423203843.2898-1-pasha.tatashin@soleen.com/
[2] https://sourceforge.net/p/makedumpfile/code/ci/master/tree/arch/arm64.c


> 
> [1/1] arm64/sparsemem: reduce SECTION_SIZE_BITS
>       https://git.kernel.org/arm64/c/f0b13ee23241
> 
> Cheers,
>