linux-kernel - Re: [PATCH 5/6] x86: mm: new tunable for single vs full TLB flush

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Date:	Mon, 07 Jul 2014 10:43:37 -0700
From:	Dave Hansen <dave@...1.net>
To:	Mel Gorman <mgorman@...e.de>
CC:	x86@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
	ak@...ux.intel.com, riel@...hat.com, alex.shi@...aro.org,
	dave.hansen@...ux.intel.com, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 5/6] x86: mm: new tunable for single vs full TLB flush

On 04/24/2014 03:37 AM, Mel Gorman wrote:
>> +Despite the fact that a single individual flush on x86 is
>> > +guaranteed to flush a full 2MB, hugetlbfs always uses the full
>> > +flushes.  THP is treated exactly the same as normal memory.
>> > +
> You are the second person that told me this and I felt the manual was
> unclear on this subject. I was told that it might be a documentation bug
> but because this discussion was in a bar I completely failed to follow up
> on it. 

For the record...  There's a new version of the Intel SDM out, and it
contains some clarifications.  They're the easiest to find in this
document which highlights the deltas from the last version:

> http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developers-manual.pdf

The documentation for invlpg itself has a new footnote, and there's also
a little bit of new text in section "4.10.2.3 Details of TLB Use".

The footnotes say:

	If the paging structures map the linear address using a page
	larger than 4 KBytes and there are multiple TLB entries for
	that page (see Section 4.10.2.3), the instruction (invlpg)
	invalidates all of them

I hope that clears up some of the ambiguity over invlpg.
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