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@xxxxxxx>
> Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
> ---
> 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