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References: <linux-mm@kvack.org> <20240416120635.361838-1-skseofh@gmail.com>
 <20240416120635.361838-2-skseofh@gmail.com> <Zh9l_LpThq9aFUR7@kernel.org>
In-Reply-To: <Zh9l_LpThq9aFUR7@kernel.org>
From: DaeRo Lee <skseofh@gmail.com>
Date: Thu, 18 Apr 2024 23:54:15 +0900
Message-ID: <CAATEi5kywwC2yUaYjgs+Gm=4HM5o=KHTqH1ALKJijWE_gge0=g@mail.gmail.com>
Subject: Re: [PATCH v2] memblock: add no-map alloc functions
To: Mike Rapoport <rppt@kernel.org>
Cc: robh@kernel.org, saravanak@google.com, akpm@linux-foundation.org, 
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, 
	Daero Lee <daero_le.lee@samsung.com>
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2024=EB=85=84 4=EC=9B=94 17=EC=9D=BC (=EC=88=98) =EC=98=A4=ED=9B=84 3:03, M=
ike Rapoport <rppt@kernel.org>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:
>
> On Tue, Apr 16, 2024 at 09:06:35PM +0900, skseofh@gmail.com wrote:
> > From: Daero Lee <daero_le.lee@samsung.com>
> >
> > Like reserved-memory with the 'no-map' property and only 'size' propert=
y
> > (w/o 'reg' property), there are memory regions need to be allocated in
> > memblock.memory marked with the MEMBLOCK_NOMAP flag, but should not be
> > allocated in memblock.reserved.
>
> This still does not explain why you need such regions.
>
> As Wei Yang explained, memblock does not allocate memory from
> memblock.reserved. The memblock.reserved array represents memory that is =
in
> use by firmware or by early kernel allocations and cannot be freed to pag=
e
> allocator.
Thank you for your comments. I used the wrong word.
When I use 'allocate', I mean that the region 'adds' to the memblock.reserv=
ed.

>
> If you have a region that's _NOMAP in memblock.memory and is absent in
> memblock.reserved it will not be mapped by the kernel page tables, but it
> will be considered as free memory by the core mm.
>
> Is this really what you want?
If my understanding is right, before freeing (memory && !reserved)
area, we marked the memblock.reserved regions and memblock.memory
regions with no-map flag. And when we free (memory && !reserved) area,
we skip the memblock.memory regions with no-map(see
should_skip_region). So, I think that the memory regions with no-map
flag will not be considered as free memory.

If there is anything I think is wrong, feel free to correct me.

Regards,
DaeRo Lee