x86_64: expand kernel stack to 16K

While I play inhouse patches with much memory pressure on qemu-kvm,
3.14 kernel was randomly crashed. The reason was kernel stack overflow.

When I investigated the problem, the callstack was a little bit deeper
by involve with reclaim functions but not direct reclaim path.

I tried to diet stack size of some functions related with alloc/reclaim
so did a hundred of byte but overflow was't disappeard so that I encounter
overflow by another deeper callstack on reclaim/allocator path.

Of course, we might sweep every sites we have found for reducing
stack usage but I'm not sure how long it saves the world(surely,
lots of developer start to add nice features which will use stack
agains) and if we consider another more complex feature in I/O layer
and/or reclaim path, it might be better to increase stack size(
meanwhile, stack usage on 64bit machine was doubled compared to 32bit
while it have sticked to 8K. Hmm, it's not a fair to me and arm64
already expaned to 16K. )

So, my stupid idea is just let's expand stack size and keep an eye
toward stack consumption on each kernel functions via stacktrace of ftrace.
For example, we can have a bar like that each funcion shouldn't exceed 200K
and emit the warning when some function consumes more in runtime.
Of course, it could make false positive but at least, it could make a
chance to think over it.

I guess this topic was discussed several time so there might be
strong reason not to increase kernel stack size on x86_64, for me not
knowing so Ccing x86_64 maintainers, other MM guys and virtio
maintainers.

Here's an example call trace using up the kernel stack:

         Depth    Size   Location    (51 entries)
         -----    ----   --------
   0)     7696      16   lookup_address
   1)     7680      16   _lookup_address_cpa.isra.3
   2)     7664      24   __change_page_attr_set_clr
   3)     7640     392   kernel_map_pages
   4)     7248     256   get_page_from_freelist
   5)     6992     352   __alloc_pages_nodemask
   6)     6640       8   alloc_pages_current
   7)     6632     168   new_slab
   8)     6464       8   __slab_alloc
   9)     6456      80   __kmalloc
  10)     6376     376   vring_add_indirect
  11)     6000     144   virtqueue_add_sgs
  12)     5856     288   __virtblk_add_req
  13)     5568      96   virtio_queue_rq
  14)     5472     128   __blk_mq_run_hw_queue
  15)     5344      16   blk_mq_run_hw_queue
  16)     5328      96   blk_mq_insert_requests
  17)     5232     112   blk_mq_flush_plug_list
  18)     5120     112   blk_flush_plug_list
  19)     5008      64   io_schedule_timeout
  20)     4944     128   mempool_alloc
  21)     4816      96   bio_alloc_bioset
  22)     4720      48   get_swap_bio
  23)     4672     160   __swap_writepage
  24)     4512      32   swap_writepage
  25)     4480     320   shrink_page_list
  26)     4160     208   shrink_inactive_list
  27)     3952     304   shrink_lruvec
  28)     3648      80   shrink_zone
  29)     3568     128   do_try_to_free_pages
  30)     3440     208   try_to_free_pages
  31)     3232     352   __alloc_pages_nodemask
  32)     2880       8   alloc_pages_current
  33)     2872     200   __page_cache_alloc
  34)     2672      80   find_or_create_page
  35)     2592      80   ext4_mb_load_buddy
  36)     2512     176   ext4_mb_regular_allocator
  37)     2336     128   ext4_mb_new_blocks
  38)     2208     256   ext4_ext_map_blocks
  39)     1952     160   ext4_map_blocks
  40)     1792     384   ext4_writepages
  41)     1408      16   do_writepages
  42)     1392      96   __writeback_single_inode
  43)     1296     176   writeback_sb_inodes
  44)     1120      80   __writeback_inodes_wb
  45)     1040     160   wb_writeback
  46)      880     208   bdi_writeback_workfn
  47)      672     144   process_one_work
  48)      528     112   worker_thread
  49)      416     240   kthread
  50)      176     176   ret_from_fork

[ Note: the problem is exacerbated by certain gcc versions that seem to
  generate much bigger stack frames due to apparently bad coalescing of
  temporaries and generating too many spills.  Rusty saw gcc-4.6.4 using
  35% more stack on the virtio path than 4.8.2 does, for example.

  Minchan not only uses such a bad gcc version (4.6.3 in his case), but
  some of the stack use is due to debugging (CONFIG_DEBUG_PAGEALLOC is
  what causes that kernel_map_pages() frame, for example). But we're
  clearly getting too close.

  The VM code also seems to have excessive stack frames partly for the
  same compiler reason, triggered by excessive inlining and lots of
  function arguments.

  We need to improve on our stack use, but in the meantime let's do this
  simple stack increase too.  Unlike most earlier reports, there is
  nothing simple that stands out as being really horribly wrong here,
  apart from the fact that the stack frames are just bigger than they
  should need to be.        - Linus ]

Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Peter Anvin <hpa@zytor.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Michael S Tsirkin <mst@redhat.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: PJ Waskiewicz <pjwaskiewicz@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>