SuperPages utilization survey

[Robert N. M. Watson]

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.
> 
> 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.
> 
> 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.
> 
> 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