linux-kernel - Re: [RFC][PATCH 03/11] x86/mm: Page size aware flush_tlb_mm

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Date:   Thu, 13 Sep 2018 11:47:59 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     will.deacon@....com, aneesh.kumar@...ux.vnet.ibm.com,
        akpm@...ux-foundation.org, npiggin@...il.com,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux@...linux.org.uk,
        heiko.carstens@...ibm.com
Subject: Re: [RFC][PATCH 03/11] x86/mm: Page size aware flush_tlb_mm_range()

>>> --- a/arch/x86/include/asm/tlbflush.h
>>> +++ b/arch/x86/include/asm/tlbflush.h
>>> @@ -507,23 +507,25 @@ struct flush_tlb_info {
>>>  	unsigned long		start;
>>>  	unsigned long		end;
>>>  	u64			new_tlb_gen;
>>> +	unsigned int		invl_shift;
>>>  };
>>
>> Maybe we really should just call this flush_stride or something.
> 
> But its a shift, not a size. stride_shift?

Yeah, sounds better than 'invl' to me.

>>>  #define local_flush_tlb() __flush_tlb()
>>>  
>>>  #define flush_tlb_mm(mm)	flush_tlb_mm_range(mm, 0UL, TLB_FLUSH_ALL, 0UL)
>>>  
>>> -#define flush_tlb_range(vma, start, end)	\
>>> -		flush_tlb_mm_range(vma->vm_mm, start, end, vma->vm_flags)
>>> +#define flush_tlb_range(vma, start, end)			\
>>> +		flush_tlb_mm_range((vma)->vm_mm, start, end,	\
>>> +				(vma)->vm_flags & VM_HUGETLB ? PMD_SHIFT : PAGE_SHIFT)
>>
>> This is safe.  But, Couldn't this PMD_SHIFT also be PUD_SHIFT for a 1G
>> hugetlb page?
> 
> It could be, but can we tell at that point?

We should have the page size via huge_page_shift(hstate_vma(vma)).  No
idea if it'll work in practice, though.