Re: [PATCH] powerpc/book3s64/radix: make tlb_single_page_flush_ceiling a debugfs entry

[Michael Ellerman <mpe@ellerman.id.au>]

"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:
> On 8/12/21 12:58 PM, Michael Ellerman wrote:
>> Christophe Leroy <christophe.leroy@csgroup.eu> writes:
>>> Le 10/08/2021 à 06:53, Aneesh Kumar K.V a écrit :
>>>> Similar to x86/s390 add a debugfs file to tune tlb_single_page_flush_ceiling.
>>>>
>>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>>>> ---
>>>>    arch/powerpc/mm/book3s64/radix_tlb.c | 48 ++++++++++++++++++++++++++++
>>>>    1 file changed, 48 insertions(+)
>>>>
>>>> diff --git a/arch/powerpc/mm/book3s64/radix_tlb.c b/arch/powerpc/mm/book3s64/radix_tlb.c
>>>> index aefc100d79a7..5cca0fe130e7 100644
>>>> --- a/arch/powerpc/mm/book3s64/radix_tlb.c
>>>> +++ b/arch/powerpc/mm/book3s64/radix_tlb.c
>>>> @@ -17,6 +17,7 @@
>> ...
>>>> +
>>>> +static int __init create_tlb_single_page_flush_ceiling(void)
>>>> +{
>>>> +	debugfs_create_file("tlb_single_page_flush_ceiling", S_IRUSR | S_IWUSR,
>>>> +			    powerpc_debugfs_root, NULL, &fops_tlbflush);
>>>
>>> Could you just use debugfs_create_u32() instead of re-implementing simple read and write ?
>> 
>> Yeah AFAICS that should work fine.
>> 
>> It could probably even be a u16?
>
> I was looking at switching all that to u64. Should i fallback to u16, 
> considering a tlb_signle_page_flush_ceiling value larger that 2**16 
> doesn't make sense?

Hmm, if we make it u16 and someone writes a value >= 2^16 it just
truncates the value to 0, which is a bit unfortunate.

So maybe just make it u32, that way if someone writes a stupidly large
value it stays large.

cheers