On Tue, 25 Sep 2012, Naoya Horiguchi wrote:

KPF_THP can be set on non-huge compound pages like slab pages, because
PageTransCompound only sees PG_head and PG_tail. Obviously this is a bug
and breaks user space applications which look for thp via /proc/kpageflags.
Currently thp is constructed only on anonymous pages, so this patch makes
KPF_THP be set when both of PageAnon and PageTransCompound are true.

Changelog in v2:
  - add a comment in code

Signed-off-by: Naoya Horiguchi <redacted>

Wouldn't PageTransCompound(page) && !PageHuge(page) && !PageSlab(page) be 
better for a future extension of thp support?

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