[PATCH] mm/sparse: remove unnecessary NULL check before allocating mem_section

[PATCH] mm/sparse: remove unnecessary NULL check before allocating mem_section

[Sang-Heon Jeon]

Commit 850ed20539a4 ("mm: move array mem_section init code out
of memory_present()") moved mem_section allocation logic
into memblocks_present().

Before that move, memory_present() could be called multiple times, so
unlikely() matched the common case, where most calls found mem_section
already allocated.

After that move, memblocks_present() is called exactly once from
sparse_init(). Under CONFIG_SPARSEMEM_EXTREME, mem_section is always
NULL when it is called.

So remove unnecessary NULL check before allocating mem_section. No
functional change.

Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
---
Hello, 

While looking into boot information, I found a minor enhancement point.
If I misunderstood anything, please feel free to let me know.

Thank you for taking valuable time to review this work.

Best Regards,
Sang-Heon Jeon
---
 mm/sparse.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index effdac6b0ab1..e13f9f5fa090 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -201,13 +201,11 @@ static void __init memblocks_present(void)
 	int i, nid;
 
 #ifdef CONFIG_SPARSEMEM_EXTREME
-	if (unlikely(!mem_section)) {
-		unsigned long size, align;
+	unsigned long size, align;
 
-		size = sizeof(struct mem_section *) * NR_SECTION_ROOTS;
-		align = 1 << (INTERNODE_CACHE_SHIFT);
-		mem_section = memblock_alloc_or_panic(size, align);
-	}
+	size = sizeof(struct mem_section *) * NR_SECTION_ROOTS;
+	align = 1 << (INTERNODE_CACHE_SHIFT);
+	mem_section = memblock_alloc_or_panic(size, align);
 #endif
 
 	for_each_mem_pfn_range(i, MAX_NUMNODES, &start, &end, &nid)
-- 
2.43.0

Re: [PATCH] mm/sparse: remove unnecessary NULL check before allocating mem_section

[Mike Rapoport]

Hi,

On Sun, Apr 19, 2026 at 11:42:25PM +0900, Sang-Heon Jeon wrote:
> Commit 850ed20539a4 ("mm: move array mem_section init code out
> of memory_present()") moved mem_section allocation logic
> into memblocks_present().
> 
> Before that move, memory_present() could be called multiple times, so
> unlikely() matched the common case, where most calls found mem_section
> already allocated.
> 
> After that move, memblocks_present() is called exactly once from
> sparse_init(). Under CONFIG_SPARSEMEM_EXTREME, mem_section is always
> NULL when it is called.
> 
> So remove unnecessary NULL check before allocating mem_section. No
> functional change.
> 
> Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>

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

> ---
> Hello, 
> 
> While looking into boot information, I found a minor enhancement point.
> If I misunderstood anything, please feel free to let me know.

I would say it's more a cleanup than enhancement :)
 
> Thank you for taking valuable time to review this work.
> 
> Best Regards,
> Sang-Heon Jeon
> ---
>  mm/sparse.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index effdac6b0ab1..e13f9f5fa090 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -201,13 +201,11 @@ static void __init memblocks_present(void)
>  	int i, nid;
>  
>  #ifdef CONFIG_SPARSEMEM_EXTREME
> -	if (unlikely(!mem_section)) {
> -		unsigned long size, align;
> +	unsigned long size, align;
>  
> -		size = sizeof(struct mem_section *) * NR_SECTION_ROOTS;
> -		align = 1 << (INTERNODE_CACHE_SHIFT);
> -		mem_section = memblock_alloc_or_panic(size, align);
> -	}
> +	size = sizeof(struct mem_section *) * NR_SECTION_ROOTS;
> +	align = 1 << (INTERNODE_CACHE_SHIFT);
> +	mem_section = memblock_alloc_or_panic(size, align);
>  #endif
>  
>  	for_each_mem_pfn_range(i, MAX_NUMNODES, &start, &end, &nid)
> -- 
> 2.43.0
> 

-- 
Sincerely yours,
Mike.

Re: [PATCH] mm/sparse: remove unnecessary NULL check before allocating mem_section

[Donet Tom]

Hi

On 4/19/26 8:12 PM, Sang-Heon Jeon wrote:
> Commit 850ed20539a4 ("mm: move array mem_section init code out
> of memory_present()") moved mem_section allocation logic
> into memblocks_present().
>
> Before that move, memory_present() could be called multiple times, so
> unlikely() matched the common case, where most calls found mem_section
> already allocated.
>
> After that move, memblocks_present() is called exactly once from
> sparse_init(). Under CONFIG_SPARSEMEM_EXTREME, mem_section is always
> NULL when it is called.
>
> So remove unnecessary NULL check before allocating mem_section. No
> functional change.
>
> Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
> ---
> Hello,
>
> While looking into boot information, I found a minor enhancement point.
> If I misunderstood anything, please feel free to let me know.
>
> Thank you for taking valuable time to review this work.
>
> Best Regards,
> Sang-Heon Jeon
> ---
>   mm/sparse.c | 10 ++++------
>   1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index effdac6b0ab1..e13f9f5fa090 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -201,13 +201,11 @@ static void __init memblocks_present(void)
>   	int i, nid;
>   
>   #ifdef CONFIG_SPARSEMEM_EXTREME
> -	if (unlikely(!mem_section)) {


LGTM

Reviewed by: Donet Tom <donettom@linux.ibm.com>

-Donet


> -		unsigned long size, align;
> +	unsigned long size, align;
>   
> -		size = sizeof(struct mem_section *) * NR_SECTION_ROOTS;
> -		align = 1 << (INTERNODE_CACHE_SHIFT);
> -		mem_section = memblock_alloc_or_panic(size, align);
> -	}
> +	size = sizeof(struct mem_section *) * NR_SECTION_ROOTS;
> +	align = 1 << (INTERNODE_CACHE_SHIFT);
> +	mem_section = memblock_alloc_or_panic(size, align);
>   #endif
>   
>   	for_each_mem_pfn_range(i, MAX_NUMNODES, &start, &end, &nid)

Re: [PATCH] mm/sparse: remove unnecessary NULL check before allocating mem_section

[Sang-Heon Jeon]

Hi

On Mon, Apr 20, 2026 at 3:49 PM Mike Rapoport <rppt@kernel.org> wrote:
>
> Hi,
>
> On Sun, Apr 19, 2026 at 11:42:25PM +0900, Sang-Heon Jeon wrote:
> > Commit 850ed20539a4 ("mm: move array mem_section init code out
> > of memory_present()") moved mem_section allocation logic
> > into memblocks_present().
> >
> > Before that move, memory_present() could be called multiple times, so
> > unlikely() matched the common case, where most calls found mem_section
> > already allocated.
> >
> > After that move, memblocks_present() is called exactly once from
> > sparse_init(). Under CONFIG_SPARSEMEM_EXTREME, mem_section is always
> > NULL when it is called.
> >
> > So remove unnecessary NULL check before allocating mem_section. No
> > functional change.
> >
> > Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
>
> Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
>
> > ---
> > Hello,
> >
> > While looking into boot information, I found a minor enhancement point.
> > If I misunderstood anything, please feel free to let me know.
>
> I would say it's more a cleanup than enhancement :)

You're right. Thanks for your kind review. That's my poor english :-(

> > Thank you for taking valuable time to review this work.
> >
> > Best Regards,
> > Sang-Heon Jeon
> > ---
> >  mm/sparse.c | 10 ++++------
> >  1 file changed, 4 insertions(+), 6 deletions(-)
> >
> > diff --git a/mm/sparse.c b/mm/sparse.c
> > index effdac6b0ab1..e13f9f5fa090 100644
> > --- a/mm/sparse.c
> > +++ b/mm/sparse.c
> > @@ -201,13 +201,11 @@ static void __init memblocks_present(void)
> >       int i, nid;
> >
> >  #ifdef CONFIG_SPARSEMEM_EXTREME
> > -     if (unlikely(!mem_section)) {
> > -             unsigned long size, align;
> > +     unsigned long size, align;
> >
> > -             size = sizeof(struct mem_section *) * NR_SECTION_ROOTS;
> > -             align = 1 << (INTERNODE_CACHE_SHIFT);
> > -             mem_section = memblock_alloc_or_panic(size, align);
> > -     }
> > +     size = sizeof(struct mem_section *) * NR_SECTION_ROOTS;
> > +     align = 1 << (INTERNODE_CACHE_SHIFT);
> > +     mem_section = memblock_alloc_or_panic(size, align);
> >  #endif
> >
> >       for_each_mem_pfn_range(i, MAX_NUMNODES, &start, &end, &nid)
> > --
> > 2.43.0
> >
>
> --
> Sincerely yours,
> Mike.

Best Regards,
Sang-Heon Jeon