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Date: Sun, 28 Apr 2024 09:33:37 +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 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:
> >
> > On Fri, Apr 19, 2024 at 10:59:52AM +0900, DaeRo Lee wrote:
> > > 2024년 4월 19일 (금) 오전 10:46, DaeRo Lee <skseofh@gmail.com>님이 작성:
> > > >
> > > > In memmap_init_reserved_pages, we mark memblock.reserved as
> > > > PageReserved first and mark the memblock.reserved with nomap flag
> > > > also.
> > > Sorry. This is my mistake. 'memblock.memory with nomap flag' is right.
> > >
> > > > -> Isn't this duplicated work? (If we add no-map region to
> > > > memblock.reserved 'and' mark in memblock.memory..)
> > > > So, I think that for the no-map region, we don't need to add to the
> > > > memblock.reserved.
> > > > This is what we do now in early_init_dt_reserve_memory. the nomap
> > > > region is not added to the memblock.reserved.
> > > >
> > > > In early_init_dt_alloc_reserved_memory_arch, if 'nomap' is true, we
> > > > mark the memblock.memory region as _NOMAP. And if the return value
> > > > 'err' is not zero(which is '-ENOMEM' from memblock_isolate_range), we
> > > > free the region.
> > > > - 'nomap' is true -> memblock_mark_nomap : success -> not free the region
> > > >
> > > > : fail -> free the region
> > > > And it can be said that we add the region to the memblock.reserved
> > > > using memblock_phys_alloc_range and if the region is nomap, then we
> > > > can free the region from memblock.reserved. But is it necessary to add
> > > > it to memblock.reserved? We just need the region in memblock.memory to
> > > > mark nomap.
> > > >
> > > > 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()

> Regards,.
> DaeRo Lee

-- 
Sincerely yours,
Mike.