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Subject: Re: [PATCH v2 14/20] mm: Provide speculative fault infrastructure
To: "Kirill A. Shutemov" <kirill@shutemov.name>,
        Laurent Dufour <ldufour@linux.vnet.ibm.com>
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On 08/27/2017 05:48 AM, Kirill A. Shutemov wrote:
>> +	/* Transparent huge pages are not supported. */
>> +	if (unlikely(pmd_trans_huge(*pmd)))
>> +		goto out_walk;
> That's looks like a blocker to me.
> 
> Is there any problem with making it supported (besides plain coding)?

IIUC we would have to reattempt once for each PMD level fault because
of the lack of a page table entry there. Besides do we want to support
huge pages in general as part of speculative page fault path ? The
number of faults will be very less (256 times lower on POWER and 512
times lower on X86). So is it worth it ? BTW calling hugetlb_fault()
after figuring out the VMA, works correctly inside handle_speculative
_fault() last time I checked.