Re: [PATCH v7 08/14] fs,x86,mpam/resctrl: Handle change in number of RMIDs on each mount

[Reinette Chatre]

Hi Tony,

On 6/9/26 2:58 PM, Luck, Tony wrote:
> On Mon, Jun 08, 2026 at 04:21:10PM -0700, Reinette Chatre wrote:
>> Hi Tony,
>>
> Changed the Subject: tag to "mpam,x86,fs/resctrl" to match what you used
> for the RFC discussion. I think the implied rule is "architectures first
> in alphabetical order, filesystem last".

After seeing the RFC discussions I do not think what I did in PoC is ideal.
MPAM is the name of the Arm feature and soon there will also be RISC-V with its
"Ssqosid" and "QBQRI" features. Since we currently have x86 as established
prefix for the PQoS and RDT features it may be more appropriate and simpler
to instead use something like "arm,riscv,x86,fs/resctrl" if such global
change is ever needed? It still follows your implied rule of "architectures
first in alphabetical order" ... but it instead actually uses the architecture
names and not a mix of feature and architecture names. I am not dictating here
and open to suggestions.

> 
>> On 6/1/26 12:56 PM, Tony Luck wrote:
...
>>> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
>>> index 327e7a863614..b374e2f84a75 100644
>>> --- a/fs/resctrl/monitor.c
>>> +++ b/fs/resctrl/monitor.c
>>> @@ -115,10 +115,17 @@ static inline struct rmid_entry *__rmid_entry(u32 idx)
>>>  
>>>  static void limbo_release_entry(struct rmid_entry *entry)
>>>  {
>>> +	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
>>
>> Having the code switch idx_limit to sometimes be resctrl_arch_system_num_rmid_idx()
>> and other times resctrl_arch_system_max_rmid_idx() makes this change difficult to
>> follow. I think it will help to use different variable names to differentiate 
>> the context in which it is being used and not leave reader trying to understand
>> why there are *two* limits.
> 
> I'll change the local variable name to max_idx_limit when dealing with
> the max value rather than the current. setup_rmid_lru_list() will have
> both variables since max_idx_limit is used for allocation, and idx_limit
> to add the right number to rmid_free_lru list. Added a comment to
> __check_limbo() explaining why max RMID is used there. I think the other
> spots are easy to see why.
What do you think of "min_idx_limit" instead of "idx_limit" to complement
the "max_idx_limit" while reflecting that it is the limit that is common 
(hence "minimum") among all monitoring resources?

Reinette