Re: [PATCH 0/3] Hugetlbfs support for riscv

[Alex Ghiti <alex@ghiti.fr>]

On 1/10/19 6:28 PM, Mike Kravetz wrote:
> On 1/10/19 12:09 AM, Alex Ghiti wrote:
>> On 1/9/19 7:23 PM, Mike Kravetz wrote:
>>> On 12/9/18 10:21 PM, Alexandre Ghiti wrote:
>>>> However I don't see any strong dependency between free_contig_range
>>>> and those configs, maybe we could allow hugetlbfs users to free boot
>>>> reserved hugepages without those configs activated, I will propose
>>>> something if Mike Kravetz agrees.
>>> Yes, that should be modified.  I think it would be a simple matter of moving
>>> free_contig_range out of that ifdef block.  If you would like, I can submit
>>> a patch for that.
>>
>> I think there is more to do: free_gigantic_page is only defined with
>> ARCH_HAS_GIGANTIC_PAGE which in turn is only defined with
>> CMA || (MEMORY_ISOLATION && COMPACTION). Moreover, if
>> ARCH_HAS_GIGANTIC_PAGE is not defined, gigantic_page_supported
>> will return false and then function like update_and_free_page will
>> not reach the call to free_gigantic_page...etc. I will send you a patch
>> when I have fixed all of that :)
> Yes, I spoke too soon :)
>
>>> Somewhat related, I do not think your patches enable dynamic allocation of
>>> gigantic pages.  Not sure if that was an oversight or conscious decision.
>>> I am not sure this is a highly used feature, but if you can do it on riscv
>>> then why not?
>> I'm not sure to understand: do you mean picking an already allocated
>> gigantic page or really allocating it with alloc_gigantic_page ? Or
>> something else ?
> The term 'dynamic allocation' may not be accurate.  Sorry!
>
> Yes, I was talking about really allocating with alloc_gigantic_page.
> It is possible to do this as long as the hstate for the gigantic page
> size already exists.  If nothing is specified on the kernel boot command
> line, the arch independent code will only set up the hstate for the default
> huge page size.  x86 has this at the end of hugetlbpage.c to create the
> gigantic page hstate as along as all config options are specified.
>
> #if (defined(CONFIG_MEMORY_ISOLATION) && defined(CONFIG_COMPACTION)) ||
> defined(CONFIG_CMA)
> static __init int gigantic_pages_init(void)
> {
> 	/* With compaction or CMA we can allocate gigantic pages at runtime */
> 	if (boot_cpu_has(X86_FEATURE_GBPAGES) && !size_to_hstate(1UL << PUD_SHIFT))
> 		hugetlb_add_hstate(PUD_SHIFT - PAGE_SHIFT);
> 	return 0;
> }
> arch_initcall(gigantic_pages_init);
> #endif
>
> I believe some other architectures do something similar to automatically
> set up hstates other huge pages sizes at boot time.  Totally optional,
> but you might want to do something like this for riscv.


Ok, I understand now, I agree that we should allow non default huge
page allocation even if not explicitly specified on kernel command line
paramter. I'll add an __init function to init hstate for gigantic page.

Thanks Mike,

Alex



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