[RFC PATCH 3/3] powerpc/mm/hugetlb: Don't enable HugeTLB if we don't have a page table cache

[Michael Ellerman]

"Aneesh Kumar K.V" <aneesh.kumar at linux.ibm.com> writes:
> On 5/16/19 8:17 PM, Michael Ellerman wrote:
>> "Aneesh Kumar K.V" <aneesh.kumar at linux.ibm.com> writes:
>>> This makes sure we don't enable HugeTLB if the cache is not configured.
>>> I am still not sure about this. IMHO hugetlb support should be a hardware
>>> support derivative and any cache allocation failure should be handled as I did
>>> in the earlier patch. But then if we were not able to create hugetlb page table
>>> cache, we can as well declare hugetlb support disabled thereby avoiding calling
>>> into allocation routines.
>>>
>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
>>> ---
>>>   arch/powerpc/mm/hugetlbpage.c | 11 +++++++++--
>>>   1 file changed, 9 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
>>> index ee16a3fb788a..4bf8bc659cc7 100644
>>> --- a/arch/powerpc/mm/hugetlbpage.c
>>> +++ b/arch/powerpc/mm/hugetlbpage.c
>>> @@ -602,6 +602,7 @@ __setup("hugepagesz=", hugepage_setup_sz);
>>>   static int __init hugetlbpage_init(void)
>>>   {
>>>   	int psize;
>>> +	bool configured = false;
>> 
>> Where's my reverse Christmas tree! :)
>
> Will fix that :)

Thanks.

>>> @@ -651,10 +652,16 @@ static int __init hugetlbpage_init(void)
>>>   
>>> -	if (IS_ENABLED(CONFIG_HUGETLB_PAGE_SIZE_VARIABLE))
>>> -		hugetlbpage_init_default();
>>> +	if (configured) {
>>> +		if (IS_ENABLED(CONFIG_HUGETLB_PAGE_SIZE_VARIABLE))
>>> +			hugetlbpage_init_default();
>>> +	} else
>>> +		pr_info("Disabling HugeTLB");
>> 
>> We're not actually doing anything to disable it in the
>> CONFIG_HUGETLB_PAGE_SIZE_VARIABLE=n case, but I guess the print is still
>> correct because we didn't enable a size in the for loop above?
>> 
>> Can we make it a bit more explicit? Maybe like:
>> 
>>    "Disabling HugeTLB, no usable page sizes found."
>> 
>
> That would confuse when they find in the dmesg
>
> [    0.000000] hash-mmu: Page sizes from device-tree: 
> [    0.000000] hash-mmu: base_shift=12: shift=12, sllp=0x0000, avpnm=0x00000000, tlbiel=1, penc=0 
> [    0.000000] hash-mmu: base_shift=12: shift=16, sllp=0x0000, avpnm=0x00000000, tlbiel=1, penc=7 
> [    0.000000] hash-mmu: base_shift=12: shift=24, sllp=0x0000, avpnm=0x00000000, tlbiel=1, penc=56 
> [    0.000000] hash-mmu: base_shift=16: shift=16, sllp=0x0110, avpnm=0x00000000, tlbiel=1, penc=1 
> [    0.000000] hash-mmu: base_shift=16: shift=24, sllp=0x0110, avpnm=0x00000000, tlbiel=1, penc=8 
> [    0.000000] hash-mmu: base_shift=24: shift=24, sllp=0x0100, avpnm=0x00000001, tlbiel=0, penc=0 
> [    0.000000] hash-mmu: base_shift=34: shift=34, sllp=0x0120, avpnm=0x000007ff, tlbiel=0, penc=3

But aren't they going to be even more confused when all we print is
"Disabling HugeTLB" with no explanation?

cheers