Re: [PATCH 1/5] pagewalk: only split huge pages when necessary

On Mon, 21 Feb 2011, Dave Hansen wrote:

v2 - rework if() block, and remove  now redundant split_huge_page()

Right now, if a mm_walk has either ->pte_entry or ->pmd_entry
set, it will unconditionally split any transparent huge pages
it runs in to.  In practice, that means that anyone doing a

	cat /proc/$pid/smaps

will unconditionally break down every huge page in the process
and depend on khugepaged to re-collapse it later.  This is
fairly suboptimal.

This patch changes that behavior.  It teaches each ->pmd_entry
handler (there are five) that they must break down the THPs
themselves.  Also, the _generic_ code will never break down
a THP unless a ->pte_entry handler is actually set.

This means that the ->pmd_entry handlers can now choose to
deal with THPs without breaking them down.

Acked-by: Mel Gorman <redacted>
Signed-off-by: Dave Hansen <redacted>

I have been running this set for serveral hours now and viewing
various smaps files is not causing wild shifts in my AnonHugePages:
counter.

Reviewed-and-tested-by: Eric B Munson [off-list ref]