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

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Message-ID: <Z9EaFhviaZHOqs8j@kernel.org>
Date: Wed, 12 Mar 2025 07:22:30 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Wei Yang <richard.weiyang@...il.com>
Cc: 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 Tue, Mar 11, 2025 at 01:41:26PM +0000, Wei Yang wrote:
> On Tue, Mar 11, 2025 at 07:27:23AM +0200, Mike Rapoport wrote:
> >> >> 
> >> >
> >> >I took another look into this commit. There maybe a very corner case in which
> >> >will leave a reserved region with no nid set.
> >> >
> >> >memmap_init_reserved_pages()
> >> >    for_each_mem_region() {
> >> >        ...
> >> >	memblock_set_node(start, end, &memblock.reserved, nid);
> >> >    }
> >> >
> >> >We leverage the iteration here to set nid to all regions in memblock.reserved.
> >> >But memblock_set_node() may call memblock_double_array() to expand the array,
> >> >which may get a range before current start. So we would miss to set the
> >> >correct nid to the new reserved region.
> >> >
> >> >I have tried to create a case in memblock test. This would happen when there
> >> >are 126 memblock.reserved regions. And the last region is across the last two
> >> >node.
> >> >
> >> >One way to fix this is compare type->max in memblock_set_node(). Then check
> >> >this return value in memmap_init_reserved_pages(). If we found the size
> >> >changes, repeat the iteration.
> >> >
> >> >But this is a very trivial one, not sure it worth fix.
> >> >
> >> 
> >> Hi, Mike
> >> 
> >> I have done a user space test which shows we may have a chance to leave a
> >> region with non-nid set.
> >> 
> >> Not sure you are ok with my approach of fixing.
> >
> >Wouldn't it be better to check for a change in reserved.max in
> >memmap_init_reserved_pages()?
> > 
> 
> Sounds better.
> 
> Previously I thought we need to hide detail from user, but actually it is
> already in memblock.c :-)
> 
> If you agree, I would like to prepare a fix.

Sure :)
 
> >> -- 
> >> Wei Yang
> >> Help you, Help me

-- 
Sincerely yours,
Mike.