vfs: Use per-cpu list for SB's s_inodes list

v6->v7:
 - Fix the race condition in __pcpu_list_next_cpu() as reported by
   Jan Kara.
 - No changes in patches 2-4.

v5->v6:
 - Remove patch 5 which can increase the kernel testing matrix.
 - Disable preemption in pcpu_list_add() as it was complained by
   the 0-day test even though it is not technically necessary.
 - Add a PERCPU_LIST_WARN_ON() macro to simplify code.
 - No changes in patches 2-4.

v4->v5:
 - Fix the UP panic problem reported by 0day test by unifying the SMP
   and UP code.
 - Add patch 5 to add a new kernel config parameter to allow disabling
   per-cpu list for small systems that won't benefit much from this
   feature.

v3->v4:
 - Fix some racing conditions in the code.
 - Add another patch from Jan to replace list_for_each_entry_safe()
   by list_for_each_entry().
 - Add lockdep annotation.

v2->v3:
 - Directly replace list_for_each_entry() and
   list_for_each_entry_safe() by pcpu_list_iterate() and
   pcpu_list_iterate_safe() respectively instead. Those 2 functions
   provide a stateful per-cpu list iteration interface.
 - Include Jan Kara's patch to clean up the fsnotify_unmount_inodes()
   function.

v1->v2:
 - Use separate structures for list head and nodes & provide a
   cleaner interface.
 - Use existing list_for_each_entry() or list_for_each_entry_safe()
   macros for each of the sb's s_inodes iteration functions instead
   of using list_for_each_entry_safe() for all of them which may not
   be safe in some cases.
 - Use an iterator interface to access all the nodes of a group of
   per-cpu lists. This approach is cleaner than the previous double-for
   macro which is kind of hacky. However, it does require more lines
   of code changes.
 - Add a preparatory patch 2 to extract out the per-inode codes from
   the superblock s_inodes list iteration functions to minimize code
   changes needed in the patch 3.

This patch is a replacement of my previous list batching patch -
https://lwn.net/Articles/674105/. Compared with the previous patch,
this one provides better performance and fairness. However, it also
requires a bit more changes in the VFS layer.

This patchset is a derivative of Andi Kleen's patch on "Initial per
cpu list for the per sb inode list"

https://git.kernel.org/cgit/linux/kernel/git/ak/linux-mis...
combined&id=f1cf9e715a40f44086662ae3b29f123cf059cbf4

Patch 1 introduces the per-cpu list.

Patch 2 cleans up the fsnotify_unmount_inodes() function by making
the code simpler and more standard.

Patch 3 replaces the use of list_for_each_entry_safe() in
evict_inodes() and invalidate_inodes() by list_for_each_entry().

Patch 4 modifies the superblock and inode structures to use the per-cpu
list. The corresponding functions that reference those structures
are modified.

Jan Kara (2):
  fsnotify: Simplify inode iteration on umount
  vfs: Remove unnecessary list_for_each_entry_safe() variants

Waiman Long (2):
  lib/percpu-list: Per-cpu list with associated per-cpu locks
  vfs: Use per-cpu list for superblock's inode list

 fs/block_dev.c              |   13 ++-
 fs/drop_caches.c            |   10 +-
 fs/fs-writeback.c           |   13 ++-
 fs/inode.c                  |   40 +++-----
 fs/notify/inode_mark.c      |   53 +++--------
 fs/quota/dquot.c            |   16 ++--
 fs/super.c                  |    7 +-
 include/linux/fs.h          |    8 +-
 include/linux/percpu-list.h |  231 +++++++++++++++++++++++++++++++++++++++++++
 lib/Makefile                |    2 +-
 lib/percpu-list.c           |  100 +++++++++++++++++++
 11 files changed, 397 insertions(+), 96 deletions(-)
 create mode 100644 include/linux/percpu-list.h
 create mode 100644 lib/percpu-list.c