[PATCH] mm/hugetlb: use kvmalloc_array for hugetlb_fault_mutex_table

[PATCH] mm/hugetlb: use kvmalloc_array for hugetlb_fault_mutex_table

[Dheeraj Kumar Srivastava]

On systems/VMs with a large number of CPUs (e.g. 4096), hugetlb_init()
computes num_fault_mutexes = roundup_pow_of_two(8 * num_possible_cpus())
= 32768.  The subsequent kmalloc for the mutex table can exceed
MAX_PAGE_ORDER when struct mutex is enlarged by debug options like
CONFIG_DEBUG_MUTEXES and CONFIG_DEBUG_LOCK_ALLOC, resulting in:

  WARNING: at __alloc_frozen_pages_noprof (order > MAX_PAGE_ORDER)
  kernel BUG at mm/hugetlb.c (BUG_ON(!hugetlb_fault_mutex_table))
  Kernel panic - not syncing: Fatal exception

Switch to kvmalloc_array() so the allocation falls back to vmalloc when
the contiguous physical allocation is too large.  The table is only
accessed by index, so virtual contiguity is sufficient.

Fixes: 8382d914ebf7 ("mm, hugetlb: improve page-fault scalability")
Signed-off-by: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
---
 mm/hugetlb.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index cea25773a6c9..f1b982595151 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4177,7 +4177,8 @@ static int __init hugetlb_init(void)
 	num_fault_mutexes = 1;
 #endif
 	hugetlb_fault_mutex_table =
-		kmalloc_objs(struct mutex, num_fault_mutexes);
+		kvmalloc_array(num_fault_mutexes,
+			       sizeof(*hugetlb_fault_mutex_table), GFP_KERNEL);
 	BUG_ON(!hugetlb_fault_mutex_table);
 
 	for (i = 0; i < num_fault_mutexes; i++)
-- 
2.25.1

Re: [PATCH] mm/hugetlb: use kvmalloc_array for hugetlb_fault_mutex_table

[Muchun Song]

> On Oct 6, 2026, at 16:02, Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com> wrote:
> 
> On systems/VMs with a large number of CPUs (e.g. 4096), hugetlb_init()
> computes num_fault_mutexes = roundup_pow_of_two(8 * num_possible_cpus())
> = 32768.  The subsequent kmalloc for the mutex table can exceed
> MAX_PAGE_ORDER when struct mutex is enlarged by debug options like
> CONFIG_DEBUG_MUTEXES and CONFIG_DEBUG_LOCK_ALLOC, resulting in:
> 
>  WARNING: at __alloc_frozen_pages_noprof (order > MAX_PAGE_ORDER)
>  kernel BUG at mm/hugetlb.c (BUG_ON(!hugetlb_fault_mutex_table))
>  Kernel panic - not syncing: Fatal exception
> 
> Switch to kvmalloc_array() so the allocation falls back to vmalloc when
> the contiguous physical allocation is too large.  The table is only
> accessed by index, so virtual contiguity is sufficient.
> 
> Fixes: 8382d914ebf7 ("mm, hugetlb: improve page-fault scalability")
> Signed-off-by: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
> ---
> mm/hugetlb.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index cea25773a6c9..f1b982595151 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4177,7 +4177,8 @@ static int __init hugetlb_init(void)
> 	num_fault_mutexes = 1;
> #endif
> 	hugetlb_fault_mutex_table =
> - 		kmalloc_objs(struct mutex, num_fault_mutexes);
> + 		kvmalloc_array(num_fault_mutexes,
> +			       sizeof(*hugetlb_fault_mutex_table), GFP_KERNEL);

Why not use kvmalloc_objs instead? A little simple.

Thanks

> 	BUG_ON(!hugetlb_fault_mutex_table);
> 
> 	for (i = 0; i < num_fault_mutexes; i++)
> -- 
> 2.25.1
> 

RE: [PATCH] mm/hugetlb: use kvmalloc_array for hugetlb_fault_mutex_table

[Srivastava, Dheeraj Kumar]

AMD General

Hi,

I will send v2.

Thanks
Dheeraj

-----Original Message-----
From: Muchun Song <muchun.song@linux.dev>
Sent: Tuesday, October 6, 2026 7:41 PM
To: Srivastava, Dheeraj Kumar <DheerajKumar.Srivastava@amd.com>
Cc: osalvador@suse.de; david@kernel.org; akpm@linux-foundation.org; davidlohr@hp.com; linux-mm@kvack.org; linux-kernel@vger.kernel.org; Hegde, Vasant <Vasant.Hegde@amd.com>; Rao, Bharata Bhasker <bharata@amd.com>
Subject: Re: [PATCH] mm/hugetlb: use kvmalloc_array for hugetlb_fault_mutex_table

[You don't often get email from muchun.song@linux.dev. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]

> On Oct 6, 2026, at 16:02, Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com> wrote:
>
> On systems/VMs with a large number of CPUs (e.g. 4096), hugetlb_init()
> computes num_fault_mutexes = roundup_pow_of_two(8 *
> num_possible_cpus()) = 32768.  The subsequent kmalloc for the mutex
> table can exceed MAX_PAGE_ORDER when struct mutex is enlarged by debug
> options like CONFIG_DEBUG_MUTEXES and CONFIG_DEBUG_LOCK_ALLOC, resulting in:
>
>  WARNING: at __alloc_frozen_pages_noprof (order > MAX_PAGE_ORDER)
> kernel BUG at mm/hugetlb.c (BUG_ON(!hugetlb_fault_mutex_table))
>  Kernel panic - not syncing: Fatal exception
>
> Switch to kvmalloc_array() so the allocation falls back to vmalloc
> when the contiguous physical allocation is too large.  The table is
> only accessed by index, so virtual contiguity is sufficient.
>
> Fixes: 8382d914ebf7 ("mm, hugetlb: improve page-fault scalability")
> Signed-off-by: Dheeraj Kumar Srivastava
> <dheerajkumar.srivastava@amd.com>
> ---
> mm/hugetlb.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c index
> cea25773a6c9..f1b982595151 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4177,7 +4177,8 @@ static int __init hugetlb_init(void)
>       num_fault_mutexes = 1;
> #endif
>       hugetlb_fault_mutex_table =
> -             kmalloc_objs(struct mutex, num_fault_mutexes);
> +             kvmalloc_array(num_fault_mutexes,
> +                            sizeof(*hugetlb_fault_mutex_table),
> + GFP_KERNEL);

Why not use kvmalloc_objs instead? A little simple.

Thanks

>       BUG_ON(!hugetlb_fault_mutex_table);
>
>       for (i = 0; i < num_fault_mutexes; i++)
> --
> 2.25.1
>