(12/19/11 3:31 PM), Dave Hansen wrote:

On 12/19/2011 11:24 AM, KOSAKI Motohiro wrote:

quoted

(12/19/11 1:38 PM), Naoya Horiguchi wrote:

quoted

This flag shows that a given pages is a subpage of transparent hugepage.
It does not care about whether it is a head page or a tail page, because
it's clear from pfn of the target page which you should know when you read
/proc/kpageflags.

Signed-off-by: Naoya Horiguchi<redacted>

NAK.

The detail of transparent hugepage are hidden by design. We hope it
keep 'transparent'.
Until any explain why we should expose KPF_THP, we don't agree it.

Transparent shouldn't mean "undebuggable", though. :)

Let's say you profiled a application and the data shows you're missing
the TLB a bunch, but you're also using THP.  This might give you a shot
at figuring out which parts of your application are *TRULY* THP-backed
instead of just the areas you *think* are backed.

I'm not sure there's another way to figure it out at the moment.

A snapshot status of THP doesn't help your purpose. I think you need
perf or similar profiling subsystem enhancement.

Because of, if you've seen KPF_THP at once, It has no guarantee to keep
hugepages until applications run. Opposite, If you only need rough
statistics, the best way is to add some new stat to
/sys/kernel/mm/transparent_hugepage.

I don't think your usecase and current proposal are matched.

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