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

["Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>]

On 5/16/19 8:17 PM, Michael Ellerman wrote:
> "Aneesh Kumar K.V" <aneesh.kumar@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@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 :)

> 
>>   	if (hugetlb_disabled) {
>>   		pr_info("HugeTLB support is disabled!\n");
>> @@ -651,10 +652,16 @@ static int __init hugetlbpage_init(void)
>>   			pgtable_cache_add(pdshift - shift);
>>   		else if (IS_ENABLED(CONFIG_PPC_FSL_BOOK3E) || IS_ENABLED(CONFIG_PPC_8xx))
>>   			pgtable_cache_add(PTE_T_ORDER);
>> +
>> +		if (!configured)
>> +			configured = true;
> 
> I'd just not worry about the if.
> 
>>   	}
>>   
>> -	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

-aneesh