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From: DaeRo Lee <skseofh@gmail.com>
Date: Sun, 28 Apr 2024 21:52:42 +0900
Message-ID: <CAATEi5=-oxOGqGD=xL=tjYRh5Q_xk5qLsXcTXq+4LRyOT8J6Rg@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 28=EC=9D=BC (=EC=9D=BC) =EC=98=A4=ED=9B=84 9:01, M=
ike Rapoport <rppt@kernel.org>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:
>
> On Sun, Apr 28, 2024 at 07:36:40PM +0900, DaeRo Lee wrote:
> > 2024=EB=85=84 4=EC=9B=94 28=EC=9D=BC (=EC=9D=BC) =EC=98=A4=ED=9B=84 3:3=
5, Mike Rapoport <rppt@kernel.org>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:
> > >
> > > On Sat, Apr 27, 2024 at 07:24:23PM +0900, DaeRo Lee wrote:
> > > > 2024=EB=85=84 4=EC=9B=94 27=EC=9D=BC (=ED=86=A0) =EC=98=A4=ED=9B=84=
 5:50, Mike Rapoport <rppt@kernel.org>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1=
:
> > > > > > >
> > > > > > > So, here is what I think:
> > > > > > > - reserved-memory w/ nomap region -> mark only to memblock.me=
mory
> > > > > > > - reserved-memory w/o nomap region -> add to the memblock.res=
erved
> > > > >
> > > > > NOMAP and memblock.reserved are semantically different, and at ma=
kes sense
> > > > > to have a "reserved nomap" node in fdt recorded in both memblock.=
memory and
> > > > > memblock.reserved.
> > > > >
> > > > > memblock.reserved represents the memory that is used by firmware =
or early
> > > > > kernel allocation, so reserved memory in fdt should be reserved i=
n memblock
> > > > > as well. I believe it's an oversight that early_init_dt_reserve_m=
emory()
> > > > > does not call memblock_reserve() for nomap memory.
> > > > >
> > > > > NOMAP is a property of a memory region that says that that region=
 should
> > > > > not be mapped in the linear map, it's not necessarily in use.
> > > >
> > > > I agree that the NOMAP region should be added to memblock.reserved.
> > > >
> > > > So, I think we need to clean-up memmap_init_reserved_pages, because=
 in
> > > > this function we call reserve_bootmem_region for memblock.reserved =
and
> > > > memblock.memory with nomap. We don't need to call
> > > > reserve_bootmem_region for nomap.
> > >
> > > Read the comment about memblock_mark_nomap()
> > I read the comment about memblock_mark_nomap() and understood that
> > regions with nomap flags should be treated as PageReserved.
> > But, if we add this nomap region to memblock.reserved, the region with
> > nomap flag will be processed in the first for-loop in
> > memmap_init_reserved_pages.
>
> memblock still must make sure that pages in nomap regions get PG_Reserved
> to be robust against potential errors and bugs in firmware parsing.
Got it.
Thank you for your comments. I'll make another patch for just clean-up
early_init_dt_reserve_memory()

Thank you.

Regards,
DaeRo Lee