From: David Woodhouse <dwmw@amazon.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@pku.edu.cn>
Suggested-by: Mike Rapoport <rppt@kernel.org>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 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

On Wed, Apr 23, 2025 at 08:52:49AM +0100, David Woodhouse wrote:
> From: David Woodhouse <dwmw@amazon.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@pku.edu.cn>
> Suggested-by: Mike Rapoport <rppt@kernel.org>
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>

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

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

-- 
Sincerely yours,
Mike.

Hi David,

On Wed, Apr 23, 2025 at 08:52:49AM +0100, David Woodhouse wrote:
> From: David Woodhouse <dwmw@amazon.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@pku.edu.cn>
> Suggested-by: Mike Rapoport <rppt@kernel.org>
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> ---

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

Tested-by: Ruihan Li <lrh2000@pku.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