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Date: Sun, 28 Apr 2024 15:00:26 +0300
From: Mike Rapoport <rppt@kernel.org>
To: DaeRo Lee <skseofh@gmail.com>
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>
Subject: Re: [PATCH v2] memblock: add no-map alloc functions
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On Sun, Apr 28, 2024 at 07:36:40PM +0900, DaeRo Lee wrote:
> 2024년 4월 28일 (일) 오후 3:35, Mike Rapoport <rppt@kernel.org>님이 작성:
> >
> > On Sat, Apr 27, 2024 at 07:24:23PM +0900, DaeRo Lee wrote:
> > > 2024년 4월 27일 (토) 오후 5:50, Mike Rapoport <rppt@kernel.org>님이 작성:
> > > > > >
> > > > > > So, here is what I think:
> > > > > > - reserved-memory w/ nomap region -> mark only to memblock.memory
> > > > > > - reserved-memory w/o nomap region -> add to the memblock.reserved
> > > >
> > > > NOMAP and memblock.reserved are semantically different, and at makes 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 in memblock
> > > > as well. I believe it's an oversight that early_init_dt_reserve_memory()
> > > > 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.
 
> Am I thinking wrong?
> 
> Regards,
> DaeRo Lee

-- 
Sincerely yours,
Mike.