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

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Message-ID: <aAjLhzrW3KsThGwF@kernel.org>
Date: Wed, 23 Apr 2025 14:14:15 +0300
From: Mike Rapoport <rppt@...nel.org>
To: David Woodhouse <dwmw2@...radead.org>
Cc: 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,
	Ruihan Li <lrh2000@....edu.cn>
Subject: Re: [PATCH v3 7/7] mm/mm_init: Use for_each_valid_pfn() in
 init_unavailable_range()

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>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.org>

> ---
>  mm/mm_init.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 

-- 
Sincerely yours,
Mike.