FROMGIT: mm/madvise: fix madvise_pageout for private file mappings

When MADV_PAGEOUT is called on a private file mapping VMA region,
we bail out early if the process is neither owner nor write capable
of the file. However, this VMA may have both private/shared clean
pages and private dirty pages. The opportunity of paging out the
private dirty pages (Anon pages) is missed. Fix this by caching
the file access check and use it later along with PageAnon() during
page walk.

We observe ~10% improvement in zram usage, thus leaving more available
memory on a 4GB RAM system running Android.

Link: https://lkml.kernel.org/r/1667971116-12900-1-git-send-email-quic_pkondeti@quicinc.com


Signed-off-by: Pavankumar Kondeti <quic_pkondeti@quicinc.com>
Cc: Charan Teja Kalla <quic_charante@quicinc.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit 8fc5be8efc3cf356f25098fbd4bda7c0e949c2ea
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git

 mm-unstable)

Bug: 259329159
Signed-off-by: Pavankumar Kondeti <quic_pkondeti@quicinc.com>
Change-Id: I5f2d425aec94e5a75ebeaf90f9f5d7adf1975c59