linux-kernel - Re: [PATCH v4 02/14] memblock: add MEMBLOCK_RSRV

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Message-ID: <20250310094238.lgsiyqci3aqdzrhj@master>
Date: Mon, 10 Mar 2025 09:42:38 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Wei Yang <richard.weiyang@...il.com>, linux-kernel@...r.kernel.org,
	Alexander Graf <graf@...zon.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
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Subject: Re: [PATCH v4 02/14] memblock: add MEMBLOCK_RSRV_KERN flag

On Mon, Mar 10, 2025 at 10:28:02AM +0200, Mike Rapoport wrote:
>Hi Wei,
>
>On Mon, Mar 10, 2025 at 07:56:27AM +0000, Wei Yang wrote:
>> On Wed, Feb 26, 2025 at 02:09:15AM +0000, Wei Yang wrote:
>> >>> 
>> >>> From the above call flow and background, there are three cases when
>> >>> memblock_alloc_range_nid() would be called:
>> >>> 
>> >>>   * If it is called before (1), memblock.reserved's nid would be adjusted correctly.
>> >>>   * If it is called after (2), we don't touch memblock.reserved.
>> >>>   * If it happens between (1) and (2), it looks would break the consistency of
>> >>>     nid information in memblock.reserved. Because when we use
>> >>>     memblock_reserve_kern(), NUMA_NO_NODE would be stored in region.
>> >>> 
>> >>> So my question is if the third case happens, would it introduce a bug? If it
>> >>> won't happen, seems we don't need to specify the nid here?
>> >>
>> >>We don't really care about proper assignment of nodes between (1) and (2)
>> >>from one side and the third case does not happen on the other side. Nothing
>> >>should call membloc_alloc() after memblock_free_all(). 
>> >>
>> >
>> >My point is if no one would call memblock_alloc() after memblock_free_all(),
>> >which set nid in memblock.reserved properly, it seems not necessary to do
>> >__memblock_reserve() with exact nid during memblock_alloc()? 
>> >
>> >As you did __memblock_reserve(found, size, nid, MEMBLOCK_RSRV_KERN) in this
>> >patch.
>> >
>> 
>> Hi, Mike
>> 
>> Do you think my understanding is reasonable?
>
>Without KHO it is indeed not strictly necessary to set nid during memblock_alloc().
>But since we anyway have nid parameter in memblock_alloc_range_nid() and it
>anyway propagates to memblock_add_range(), I think it's easier and cleaner
>to pass nid to __memblock_reserve() there.
>
>And for KHO estimation of scratch size it is important to have nid assigned to
>the reserved areas before memblock_free_all(), at least for the allocations
>that request particular nid explicitly.

Thanks, I see your point.

> 
>> -- 
>> Wei Yang
>> Help you, Help me
>
>-- 
>Sincerely yours,
>Mike.

-- 
Wei Yang
Help you, Help me