FROMLIST: mm: smaps: split PSS into components

Report separate components (anon, file, and shmem)
for PSS in smaps and smaps_rollup.

This helps understand and tune the memory manager behavior
in consumer devices, particularly mobile devices.  Many of
them (e.g. chromebooks and Android-based devices) use zram
for anon memory, and perform disk reads for discarded file
pages.  The difference in latency is large (e.g. reading
a single page from SSD is 30 times slower than decompressing
a zram page on one popular device), thus it is useful to know
how much of the PSS is anon vs. file.

This patch also removes a small code duplication in smaps_account,
which would have gotten worse otherwise.

(am from https://patchwork.kernel.org/patch/10969398/

)

BUG=chromium:962973
TEST=ran it

Change-Id: Icaa696746d5e83b993c936fa28ff93a6a9dfad4e
Signed-off-by: Luigi Semenzato <semenzato@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1660016


Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Sonny Rao <sonnyrao@chromium.org>
Reviewed-by: Julan Hsu <julanhsu@google.com>