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

[DaeRo Lee <skseofh@gmail.com>]

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2024년 4월 27일 (토) 오전 11:42, DaeRo Lee <skseofh@gmail.com>님이 작성:

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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
>

Sorry for wrong email format.
I just re-send this for kernel mailing loop.

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