[PATCH v2] fs/resctrl: Allocate rmid_ptrs[] using kvzalloc_objs()

[PATCH v2] fs/resctrl: Allocate rmid_ptrs[] using kvzalloc_objs()

[Ben Horgan]

On an MPAM system the number of entries in rmid_ptrs[] is the number of PARTIDs
multiplied by the number of PMGs. The maximum possible number of PARTIDs is
0x10000 and the maximum number of PMGs is 0x100. On a system pushing the limits
of the MPAM specification this can be large enough to consistently fail the
kzalloc_objs() allocation and hence fail to mount the resctrl filesystem.

Switch to allocating rmid_ptrs[] using kvzalloc_objs() so that large allocations
fall back to vmalloc().

Fixes: 264c285999fc ("arm_mpam: resctrl: Add monitor initialisation and domain boilerplate")
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
---
I found this by testing the extremes of a software model and don't expect this
to effect real systems.
---
 fs/resctrl/monitor.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
index 73413cb128ea..2d7df60973d1 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -979,7 +979,7 @@ int setup_rmid_lru_list(void)
 		return 0;
 
 	idx_limit = resctrl_arch_system_num_rmid_idx();
-	rmid_ptrs = kzalloc_objs(struct rmid_entry, idx_limit);
+	rmid_ptrs = kvzalloc_objs(struct rmid_entry, idx_limit);
 	if (!rmid_ptrs)
 		return -ENOMEM;
 
@@ -1010,7 +1010,7 @@ void free_rmid_lru_list(void)
 		return;
 
 	mutex_lock(&rdtgroup_mutex);
-	kfree(rmid_ptrs);
+	kvfree(rmid_ptrs);
 	rmid_ptrs = NULL;
 	mutex_unlock(&rdtgroup_mutex);
 }
-- 
2.43.0

Re: [PATCH v2] fs/resctrl: Allocate rmid_ptrs[] using kvzalloc_objs()

[Ben Horgan]

I realised I forgot to include a changelog with this v2. The only change from v1 is an update to the
fixes tag as suggested by Reinette.

Thanks,

Ben

On 11/09/2026 17:06, Ben Horgan wrote:
> On an MPAM system the number of entries in rmid_ptrs[] is the number of PARTIDs
> multiplied by the number of PMGs. The maximum possible number of PARTIDs is
> 0x10000 and the maximum number of PMGs is 0x100. On a system pushing the limits
> of the MPAM specification this can be large enough to consistently fail the
> kzalloc_objs() allocation and hence fail to mount the resctrl filesystem.
> 
> Switch to allocating rmid_ptrs[] using kvzalloc_objs() so that large allocations
> fall back to vmalloc().
> 
> Fixes: 264c285999fc ("arm_mpam: resctrl: Add monitor initialisation and domain boilerplate")
> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> ---
> I found this by testing the extremes of a software model and don't expect this
> to effect real systems.
> ---
>  fs/resctrl/monitor.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
> index 73413cb128ea..2d7df60973d1 100644
> --- a/fs/resctrl/monitor.c
> +++ b/fs/resctrl/monitor.c
> @@ -979,7 +979,7 @@ int setup_rmid_lru_list(void)
>  		return 0;
>  
>  	idx_limit = resctrl_arch_system_num_rmid_idx();
> -	rmid_ptrs = kzalloc_objs(struct rmid_entry, idx_limit);
> +	rmid_ptrs = kvzalloc_objs(struct rmid_entry, idx_limit);
>  	if (!rmid_ptrs)
>  		return -ENOMEM;
>  
> @@ -1010,7 +1010,7 @@ void free_rmid_lru_list(void)
>  		return;
>  
>  	mutex_lock(&rdtgroup_mutex);
> -	kfree(rmid_ptrs);
> +	kvfree(rmid_ptrs);
>  	rmid_ptrs = NULL;
>  	mutex_unlock(&rdtgroup_mutex);
>  }

Re: [PATCH v2] fs/resctrl: Allocate rmid_ptrs[] using kvzalloc_objs()

[Reinette Chatre]

Hi Ben,

On 9/11/26 9:06 AM, Ben Horgan wrote:
> On an MPAM system the number of entries in rmid_ptrs[] is the number of PARTIDs
> multiplied by the number of PMGs. The maximum possible number of PARTIDs is
> 0x10000 and the maximum number of PMGs is 0x100. On a system pushing the limits
> of the MPAM specification this can be large enough to consistently fail the
> kzalloc_objs() allocation and hence fail to mount the resctrl filesystem.
> 
> Switch to allocating rmid_ptrs[] using kvzalloc_objs() so that large allocations
> fall back to vmalloc().
> 
> Fixes: 264c285999fc ("arm_mpam: resctrl: Add monitor initialisation and domain boilerplate")
> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> ---
> I found this by testing the extremes of a software model and don't expect this
> to effect real systems.
> ---
>  fs/resctrl/monitor.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
> index 73413cb128ea..2d7df60973d1 100644
> --- a/fs/resctrl/monitor.c
> +++ b/fs/resctrl/monitor.c
> @@ -979,7 +979,7 @@ int setup_rmid_lru_list(void)
>  		return 0;
>  
>  	idx_limit = resctrl_arch_system_num_rmid_idx();
> -	rmid_ptrs = kzalloc_objs(struct rmid_entry, idx_limit);
> +	rmid_ptrs = kvzalloc_objs(struct rmid_entry, idx_limit);
>  	if (!rmid_ptrs)
>  		return -ENOMEM;
>  

resctrl_arch_system_num_rmid_idx() that guides the rmid_ptrs[] allocation is
also used to size the L3 monitoring state rdt_l3_mon_domain::rmid_busy_llc[]
and rdt_l3_mon_domain::mbm_states[]. Each RMID is expected to have associated
states in these structures so to fully support this their allocation needs
to change also? I did a quick check and there does not seem to be a
vmalloc variant for bitmap allocation though so that may need to be
customized or created.

Reinette

Re: [PATCH v2] fs/resctrl: Allocate rmid_ptrs[] using kvzalloc_objs()

[Ben Horgan]

Hi Reinette,

On 16/09/2026 17:52, Reinette Chatre wrote:
> Hi Ben,
> 
> On 9/11/26 9:06 AM, Ben Horgan wrote:
>> On an MPAM system the number of entries in rmid_ptrs[] is the number of PARTIDs
>> multiplied by the number of PMGs. The maximum possible number of PARTIDs is
>> 0x10000 and the maximum number of PMGs is 0x100. On a system pushing the limits
>> of the MPAM specification this can be large enough to consistently fail the
>> kzalloc_objs() allocation and hence fail to mount the resctrl filesystem.
>>
>> Switch to allocating rmid_ptrs[] using kvzalloc_objs() so that large allocations
>> fall back to vmalloc().
>>
>> Fixes: 264c285999fc ("arm_mpam: resctrl: Add monitor initialisation and domain boilerplate")
>> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
>> Reviewed-by: Tony Luck <tony.luck@intel.com>
>> ---
>> I found this by testing the extremes of a software model and don't expect this
>> to effect real systems.
>> ---
>>  fs/resctrl/monitor.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
>> index 73413cb128ea..2d7df60973d1 100644
>> --- a/fs/resctrl/monitor.c
>> +++ b/fs/resctrl/monitor.c
>> @@ -979,7 +979,7 @@ int setup_rmid_lru_list(void)
>>  		return 0;
>>  
>>  	idx_limit = resctrl_arch_system_num_rmid_idx();
>> -	rmid_ptrs = kzalloc_objs(struct rmid_entry, idx_limit);
>> +	rmid_ptrs = kvzalloc_objs(struct rmid_entry, idx_limit);
>>  	if (!rmid_ptrs)
>>  		return -ENOMEM;
>>  
> 
> resctrl_arch_system_num_rmid_idx() that guides the rmid_ptrs[] allocation is
> also used to size the L3 monitoring state rdt_l3_mon_domain::rmid_busy_llc[]
> and rdt_l3_mon_domain::mbm_states[]. Each RMID is expected to have associated
> states in these structures so to fully support this their allocation needs
> to change also? 

At least, rdt_l3_mon_domain::mbm_states[] should use kvcalloc. I realise that I didn't hit this on
the model I was using to test this didn't have memory bandwidth monitors.

For, rdt_l3_mon_domain::rmid_busy_llc[] the allocation will have succeeded on a model as there are
cache occupancy counters. The allocation here is smaller than the others as it allocates a bit per
RMID rather than multiple bytes per RMID like the other two allocations. This gives a limit here of
0x100 * 0x10000 / 0x8 = 0x200000 bytes, 2MB. My view here would be that, although this is quite big,
it's not standing in the way of testing on a model and physical systems even approaching this size
are not likely to ever be built and so doesn't justify either open coding the bitmap allocation and
freeing or creating a new bitmap allocator. Does that make sense?

> I did a quick check and there does not seem to be a
> vmalloc variant for bitmap allocation though so that may need to be
> customized or created.

Yeah, I don't see one either.

Thanks,

Ben>
> Reinette
> 
> 
> 

Re: [PATCH v2] fs/resctrl: Allocate rmid_ptrs[] using kvzalloc_objs()

[Reinette Chatre]

Hi Ben,

On 9/17/26 9:15 AM, Ben Horgan wrote:
> On 16/09/2026 17:52, Reinette Chatre wrote:
>> On 9/11/26 9:06 AM, Ben Horgan wrote:
>>> On an MPAM system the number of entries in rmid_ptrs[] is the number of PARTIDs
>>> multiplied by the number of PMGs. The maximum possible number of PARTIDs is
>>> 0x10000 and the maximum number of PMGs is 0x100. On a system pushing the limits
>>> of the MPAM specification this can be large enough to consistently fail the
>>> kzalloc_objs() allocation and hence fail to mount the resctrl filesystem.
>>>
>>> Switch to allocating rmid_ptrs[] using kvzalloc_objs() so that large allocations
>>> fall back to vmalloc().
>>>
>>> Fixes: 264c285999fc ("arm_mpam: resctrl: Add monitor initialisation and domain boilerplate")
>>> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
>>> Reviewed-by: Tony Luck <tony.luck@intel.com>
>>> ---
>>> I found this by testing the extremes of a software model and don't expect this
>>> to effect real systems.
>>> ---
>>>  fs/resctrl/monitor.c | 4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
>>> index 73413cb128ea..2d7df60973d1 100644
>>> --- a/fs/resctrl/monitor.c
>>> +++ b/fs/resctrl/monitor.c
>>> @@ -979,7 +979,7 @@ int setup_rmid_lru_list(void)
>>>  		return 0;
>>>  
>>>  	idx_limit = resctrl_arch_system_num_rmid_idx();
>>> -	rmid_ptrs = kzalloc_objs(struct rmid_entry, idx_limit);
>>> +	rmid_ptrs = kvzalloc_objs(struct rmid_entry, idx_limit);
>>>  	if (!rmid_ptrs)
>>>  		return -ENOMEM;
>>>  
>>
>> resctrl_arch_system_num_rmid_idx() that guides the rmid_ptrs[] allocation is
>> also used to size the L3 monitoring state rdt_l3_mon_domain::rmid_busy_llc[]
>> and rdt_l3_mon_domain::mbm_states[]. Each RMID is expected to have associated
>> states in these structures so to fully support this their allocation needs
>> to change also? 
> 
> At least, rdt_l3_mon_domain::mbm_states[] should use kvcalloc. I realise that I didn't hit this on
> the model I was using to test this didn't have memory bandwidth monitors.
> 
> For, rdt_l3_mon_domain::rmid_busy_llc[] the allocation will have succeeded on a model as there are
> cache occupancy counters. The allocation here is smaller than the others as it allocates a bit per
> RMID rather than multiple bytes per RMID like the other two allocations. This gives a limit here of
> 0x100 * 0x10000 / 0x8 = 0x200000 bytes, 2MB. My view here would be that, although this is quite big,
> it's not standing in the way of testing on a model and physical systems even approaching this size
> are not likely to ever be built and so doesn't justify either open coding the bitmap allocation and
> freeing or creating a new bitmap allocator. Does that make sense?

I think this may still stand in the way of testing on a model since it depends on when that testing
onlines the domains and how fragmented the memory is at that time. A simple "boot with all domains
already online" may be ok but I am not sure.

Reinette