On 06/28/2012 08:55 AM, Andrea Arcangeli wrote:

gup_fast will skip over non present ptes (pte_numa requires the pte to
be non present). So no explicit check is needed for pte_numa in the
pte case.

gup_fast will also automatically skip over THP when the trans huge pmd
is non present (pmd_numa requires the pmd to be non present).

But for the special pmd mode scan of knuma_scand
(/sys/kernel/mm/autonuma/knuma_scand/pmd == 1), the pmd may be of numa
type (so non present too), the pte may be present. gup_pte_range
wouldn't notice the pmd is of numa type. So to avoid losing a NUMA
hinting page fault with gup_fast we need an explicit check for
pmd_numa() here to be sure it will fault through gup ->
handle_mm_fault.

Signed-off-by: Andrea Arcangeli<redacted>

Assuming pmd_numa will get the documentation I asked for a few
patches back, this patch is fine, since people will just be able
to look at a nice comment above pmd_numa and see what is going on.

Acked-by: Rik van Riel <redacted>

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