linux-kernel - Re: [PATCH v3 7/7] mm/mm_init: Use for_each_valid_pfn() in init_unavailable

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Message-ID: <rp7ftbfx7kbdh4xe3ptrzx2dakwjjo3npn6b6l4wjn5zj3n5t6@cij3nx67r3av>
Date: Wed, 23 Apr 2025 17:35:49 +0800
From: Ruihan Li <lrh2000@....edu.cn>
To: David Woodhouse <dwmw2@...radead.org>
Cc: Mike Rapoport <rppt@...nel.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, "Sauerwein, David" <dssauerw@...zon.de>, 
	Anshuman Khandual <anshuman.khandual@....com>, Ard Biesheuvel <ardb@...nel.org>, 
	Catalin Marinas <catalin.marinas@....com>, David Hildenbrand <david@...hat.com>, 
	Marc Zyngier <maz@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Mike Rapoport <rppt@...ux.ibm.com>, Will Deacon <will@...nel.org>, kvmarm@...ts.cs.columbia.edu, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v3 7/7] mm/mm_init: Use for_each_valid_pfn() in
 init_unavailable_range()

Hi David,

On Wed, Apr 23, 2025 at 08:52:49AM +0100, David Woodhouse wrote:
> From: David Woodhouse <dwmw@...zon.co.uk>
> 
> Currently, memmap_init initializes pfn_hole with 0 instead of
> ARCH_PFN_OFFSET. Then init_unavailable_range will start iterating each
> page from the page at address zero to the first available page, but it
> won't do anything for pages below ARCH_PFN_OFFSET because pfn_valid
> won't pass.
> 
> If ARCH_PFN_OFFSET is very large (e.g., something like 2^64-2GiB if the
> kernel is used as a library and loaded at a very high address), the
> pointless iteration for pages below ARCH_PFN_OFFSET will take a very
> long time, and the kernel will look stuck at boot time.
> 
> Use for_each_valid_pfn() to skip the pointless iterations.
> 
> Reported-by: Ruihan Li <lrh2000@....edu.cn>
> Suggested-by: Mike Rapoport <rppt@...nel.org>
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> ---

Thanks! I have confirmed that this worked in my scenario and fixed the
problem I reported earlier.

Tested-by: Ruihan Li <lrh2000@....edu.cn>

>  mm/mm_init.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 41884f2155c4..0d1a4546825c 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -845,11 +845,7 @@ static void __init init_unavailable_range(unsigned long spfn,
>  	unsigned long pfn;
>  	u64 pgcnt = 0;
>  
> -	for (pfn = spfn; pfn < epfn; pfn++) {
> -		if (!pfn_valid(pageblock_start_pfn(pfn))) {
> -			pfn = pageblock_end_pfn(pfn) - 1;
> -			continue;
> -		}
> +	for_each_valid_pfn(pfn, spfn, epfn) {
>  		__init_single_page(pfn_to_page(pfn), pfn, zone, node);
>  		__SetPageReserved(pfn_to_page(pfn));
>  		pgcnt++;
> -- 
> 2.49.0

Thanks,
Ruihan Li