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

[DaeRo Lee <skseofh@gmail.com>]

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2024년 4월 19일 (금) 오전 10:59, DaeRo Lee <skseofh@gmail.com>님이 작성:

> 2024년 4월 19일 (금) 오전 10:46, DaeRo Lee <skseofh@gmail.com>님이 작성:
> >
> > 2024년 4월 19일 (금) 오전 3:04, Mike Rapoport <rppt@kernel.org>님이 작성:
> > >
> > > On Thu, Apr 18, 2024 at 11:54:15PM +0900, DaeRo Lee wrote:
> > > > 2024년 4월 17일 (수) 오후 3:03, Mike Rapoport <rppt@kernel.org>님이 작성:
> > > > >
> > > > > 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'
> property
> > > > > > (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 page
> > > > > allocator.
> > > > Thank you for your comments. I used the wrong word.
> > > > When I use 'allocate', I mean that the region 'adds' to the
> memblock.reserved.
> > > >
> > > > >
> > > > > 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.
> > >
> > > You are right here.
> > >
> > > But I still don't understand *why* do you want to change the way
> > > early_init_dt_alloc_reserved_memory_arch() works.
> >
> > 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
> >
> > Regards,
> > DaeRo Lee
>

Hello
Can I get your opinions about this?
It will be very helpful to improve my understanding of memblock and
reserved region.

Thank you

>

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