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From: "Robert N. M. Watson" <rwatson@freebsd.org>
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Date: Sat, 9 Jun 2012 13:36:28 +0100
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To: Konstantin Belousov <kostikbel@gmail.com>
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Subject: Re: SuperPages utilization survey
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On 9 Jun 2012, at 11:05, Konstantin Belousov wrote:

> First, there is nothing which would prevent demotion from happens =
while
> you iterate over the map, so you could get funyy numbers, like 42 =
superpages
> for 2M region with your method.
>=20
> Second, the superpage size if machine-depended, and even single =
machine
> could support differently sized superpage. For amd64, hardware can =
support
> 2M and 1G pages, and for i386 you can get 4M or 2M depending on PAE =
config.
>=20
> And last, I in fact do not see much use for any 'superpage count'. =
Would I
> would like to see is the TLB miss count for a region. Then I could =
estimate
> whether superpage enabling provided some advantage. Just as a note, if
> there were no accesses to a region after promotion, then promotion is
> the waste.
>=20
> Anyway, please do not consider this as discouraging you from doing a
> useful work.

Despite the rendering and underlying semantic issues, I admit that I =
would like to know when superpages are being used by processes -- =
perhaps enough information to construct a histogram of page sizes for =
each mapping.

Robert=