linux-kernel - Re: [PATCH v2] memblock: add no-map alloc functions

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Date: Sat, 27 Apr 2024 19:24:23 +0900
From: DaeRo Lee <skseofh@...il.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: robh@...nel.org, saravanak@...gle.com, akpm@...ux-foundation.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	Daero Lee <daero_le.lee@...sung.com>
Subject: Re: [PATCH v2] memblock: add no-map alloc functions

2024년 4월 27일 (토) 오후 5:50, Mike Rapoport <rppt@...nel.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@...il.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.

Regards,.
DaeRo Lee