linux-kernel - Re: [PATCH 0/2] of: remove reserved regions count restriction

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Message-ID: <YZoK4IiBOTPduEyN@debian>
Date:   Sun, 21 Nov 2021 17:01:20 +0800
From:   Calvin Zhang <calvinzhang.cool@...il.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Vineet Gupta <vgupta@...nel.org>,
        Russell King <linux@...linux.org.uk>,
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Subject: Re: [PATCH 0/2] of: remove reserved regions count restriction

On Sun, Nov 21, 2021 at 08:43:47AM +0200, Mike Rapoport wrote:
>On Fri, Nov 19, 2021 at 03:58:17PM +0800, Calvin Zhang wrote:
>> The count of reserved regions in /reserved-memory was limited because
>> the struct reserved_mem array was defined statically. This series sorts
>> out reserved memory code and allocates that array from early allocator.
>> 
>> Note: reserved region with fixed location must be reserved before any
>> memory allocation. While struct reserved_mem array should be allocated
>> after allocator is activated. We make early_init_fdt_scan_reserved_mem()
>> do reservation only and add another call to initialize reserved memory.
>> So arch code have to change for it.
>
>I think much simpler would be to use the same constant for sizing
>memblock.reserved and reserved_mem arrays.
>
>If there is too much reserved regions in the device tree, reserving them in
>memblock will fail anyway because memblock also starts with static array
>for memblock.reserved, so doing one pass with memblock_reserve() and
>another to set up reserved_mem wouldn't help anyway.

Yes. This happens only if there are two many fixed reserved regions.
memblock.reserved can be resized after paging.

I also find another problem. Initializing dynamic reservation after
paging would fail to mark it no-map because no-map flag works when doing
direct mapping. This seems to be a circular dependency.

Thank You,
Calvin