Re: [PATCH v12 14/25] fs/resctrl: Rebuild free RMID list on each mount

["Moger, Babu" <bmoger@amd.com>]

Hi Tony,

On 9/22/2026 3:30 PM, Luck, Tony wrote:
> On Mon, Sep 21, 2026 at 12:45:56PM -0500, Babu Moger wrote:
>> Hi Tony,
> 
> Hi Babu,
> 
> Thanks for running tests to make sure that I didn't break any AMD
> functionality, and for reviewing these patches.
> 
>>
>>>    int setup_rmid_lru_list(void)
>>>    {
>>> -	struct rmid_entry *entry = NULL;
>>> -	u32 idx_limit;
>>> -	u32 idx;
>>> +	struct rmid_entry *entry;
>>> +	u32 cur_idx_limit;
>>> +	u32 rsvd_idx;
>>>    	int i;
>>>    	if (!resctrl_mon_capable())
>>>    		return 0;
>>>    	/*
>>> -	 * Called on every mount, but the number of RMIDs cannot change
>>> -	 * after the first mount, so keep using the same set of rmid_ptrs[]
>>> -	 * until resctrl_exit(). Note that the limbo handler continues to
>>> -	 * access rmid_ptrs[] after resctrl is unmounted.
>>> +	 * Allocate the largest number of RMIDs that this system will ever
>>> +	 * need. These cannot be freed until resctrl_exit() because the limbo
>>> +	 * handler continues to access rmid_ptrs[] after resctrl is unmounted.
>>>    	 */
>>> -	if (rmid_ptrs)
>>> -		return 0;
>>> +	if (!rmid_ptrs) {
>>> +		num_rmid_ptrs = resctrl_arch_system_max_rmid_idx();
>>> +		rmid_ptrs = kzalloc_objs(struct rmid_entry, num_rmid_ptrs);
>>> +		if (!rmid_ptrs) {
>>> +			num_rmid_ptrs = 0;
>>> +			return -ENOMEM;
>>> +		}
>>> -	idx_limit = resctrl_arch_system_max_rmid_idx();
>>> -	rmid_ptrs = kzalloc_objs(struct rmid_entry, idx_limit);
>>> -	if (!rmid_ptrs)
>>> -		return -ENOMEM;
>>> +		for (i = 0; i < num_rmid_ptrs; i++) {
>>> +			entry = &rmid_ptrs[i];
>>> +			INIT_LIST_HEAD(&entry->list);
>>> -	for (i = 0; i < idx_limit; i++) {
>>> -		entry = &rmid_ptrs[i];
>>> -		INIT_LIST_HEAD(&entry->list);
>>> +			resctrl_arch_rmid_idx_decode(i, &entry->closid, &entry->rmid);
>>> +		}
>>> +	}
>>> -		resctrl_arch_rmid_idx_decode(i, &entry->closid, &entry->rmid);
>>> -		list_add_tail(&entry->list, &rmid_free_lru);
>>> +	/* Find how many RMIDs are available for this mount */
>>> +	cur_idx_limit = resctrl_arch_system_num_rmid_idx();
>>> +	if (cur_idx_limit > num_rmid_ptrs) {
>>> +		pr_warn_once("RMID count %u exceeds allocated %u; capping\n",
>>> +			     cur_idx_limit, num_rmid_ptrs);
>>> +		cur_idx_limit = num_rmid_ptrs;
>>>    	}
>>> +	INIT_LIST_HEAD(&rmid_free_lru);
>>
>> It is possible the list is not empty at this point with difference in
>> numbers from one mount to another?  Should you check if the list is empty
>> and clean it up?
> 
> After a clean unmount the free list will likely be mostly full as
> resctrl_fs_teardown() calls rmdir_all_sub() which is going to free
> up RMIDs as directories are removed. The only RMIDs missing will be
> the ones in limbo waiting for LLC occupancy counts to decay.
> 
> But the free list may contain some RMIDs that are out of range for the
> new mount. Simply rebuilding the free list from scratch is one option
> to resolve this. Another would be to walk the list add remove any
> RMIDs out of range for the new mount.

Either is fine.

Will something like this work?

list_for_each_entry_safe(entry, tmp, &rmid_free_lru, list)
              list_del(&entry->list);
INIT_LIST_HEAD(&rmid_free_lru);

Thanks
Babu