Re: [V2] powerpc/Kconfig: Update config option based on page size.

[santhosh <santhog4@linux.vnet.ibm.com>]

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> Michael Ellerman <mpe@ellerman.id.au> writes:
>
>> On Fri, 2016-19-02 at 05:38:47 UTC, Rashmica Gupta wrote:
>>> Currently on PPC64 changing kernel pagesize from 4K to 64K leaves
>>> FORCE_MAX_ZONEORDER set to 13 - which produces a compile error.
>>>
>> ...
>>> So, update the range of FORCE_MAX_ZONEORDER from 9-64 to 8-9 for 64K pages
>>> and from 13-64 to 9-13 for 4K pages.
>>>
>>> Signed-off-by: Rashmica Gupta <rashmicy@gmail.com>
>>> Reviewed-by: Balbir Singh <bsingharora@gmail.com>
>> Applied to powerpc next, thanks.
>>
>> https://git.kernel.org/powerpc/c/a7ee539584acf4a565b7439cea
>>
> HPAGE_PMD_ORDER is not something we should check w.r.t 4k linux page
> size. We do have the below constraint w.r.t hugetlb pages
>
> static inline bool hstate_is_gigantic(struct hstate *h)
> {
> 	return huge_page_order(h) >= MAX_ORDER;
> }
>
> That require MAX_ORDER to be greater than 12.
>
> Did we test hugetlbfs 4k config with this patch ? Will it work if we
> start marking hugepage as gigantic page ?
>
> -aneesh
>
Hello Rashmica,

With upstream linux kernel 4.8.0-rc1-00006-gbae9cc6 compiled with linux 
4k page size we are not able set hugepages, Aneesh had a look at the 
problem and he mentioned this commit is causing the issue.

*Details:*
We are using pkvm ubuntu 16.04 guest with upstream kernel 
[4.8.0-rc1-00006-gbae9cc6] compiled with  4k page size

o/p from guest:
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:      16384 kB

Page sizes from device-tree: [dmesg]
[    0.000000] base_shift=12: shift=12, sllp=0x0000, avpnm=0x00000000, 
tlbiel=1, penc=0
[    0.000000] base_shift=12: shift=24, sllp=0x0000, avpnm=0x00000000, 
tlbiel=1, penc=56
[    0.000000] base_shift=24: shift=24, sllp=0x0100, avpnm=0x00000001, 
tlbiel=0, penc=0

while trying to configure the hugepages inside the guest it throws the 
below error:

echo 100 > /proc/sys/vm/nr_hugepages
-bash: echo: write error: Invalid argument

*Note*: we do not see the problem when the linux page is 64k

Thanks,
Santhosh G


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