Currently, we store each page's allocation stacktrace on corresponding
page_ext structure and it requires a lot of memory.  This causes the
problem that memory tight system doesn't work well if page_owner is
enabled.  Moreover, even with this large memory consumption, we cannot
get full stacktrace because we allocate memory at boot time and just
maintain 8 stacktrace slots to balance memory consumption.  We could
increase it to more but it would make system unusable or change system
behaviour.

To solve the problem, this patch uses stackdepot to store stacktrace.
It obviously provides memory saving but there is a drawback that
stackdepot could fail.

stackdepot allocates memory at runtime so it could fail if system has
not enough memory.  But, most of allocation stack are generated at very
early time and there are much memory at this time.  So, failure would
not happen easily.  And, one failure means that we miss just one page's
allocation stacktrace so it would not be a big problem.  In this patch,
when memory allocation failure happens, we store special stracktrace
handle to the page that is failed to save stacktrace.  With it, user can
guess memory usage properly even if failure happens.

Memory saving looks as following.  (4GB memory system with page_owner)
(before the patch -> after the patch)

static allocation:
92274688 bytes -> 25165824 bytes

dynamic allocation after boot + kernel build:
0 bytes -> 327680 bytes

total:
92274688 bytes -> 25493504 bytes

72% reduction in total.

Note that implementation looks complex than someone would imagine
because there is recursion issue.  stackdepot uses page allocator and
page_owner is called at page allocation.  Using stackdepot in page_owner
could re-call page allcator and then page_owner.  That is a recursion.
To detect and avoid it, whenever we obtain stacktrace, recursion is
checked and page_owner is set to dummy information if found.  Dummy
information means that this page is allocated for page_owner feature
itself (such as stackdepot) and it's understandable behavior for user.

[iamjoonsoo.kim@lge.com: mm-page_owner-use-stackdepot-to-store-stacktrace-v3]
  Link: http://lkml.kernel.org/r/1464230275-25791-6-git-send-email-iamjoonsoo.kim@lge.com
  Link: http://lkml.kernel.org/r/1466150259-27727-7-git-send-email-iamjoonsoo.kim@lge.com
Link: http://lkml.kernel.org/r/1464230275-25791-6-git-send-email-iamjoonsoo.kim@lge.com


Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>