[PATCH v8 0/6] vfs: Use dlock list for SB's s_inodes list

[Waiman Long]

v7->v8:
 - Integrate the additional patches 8, 9 and 10 sent to fix issues in
   the original v7 patchset into patch 1 and adjust the other patches
   accordingly.

v6->v7:
 - Fix outdated email address.
 - Add a comment to patch 4 to explain allocation issue & fix a
   compilation problem with cpumask.
 - Replace patch 6 with another one that adds an irqsafe mode argument 
   in alloc_dlock_list_heads() instead of adding new APIs.

v5->v6:
 - Rebased the patch to 4.14-rc3.
 - Drop the fsnotify patch as it had been merged somehow.
 - Add a new patch 5 with alternative way of selecting list by hashing
   instead of cpu #.
 - Add a new patch 6 to proivde a set irq safe APIs to be used in
   interrupt context.
 - Update the CPU to index mapping code.

v4->v5:
 - Rebased the patch to 4.8-rc1 (changes to fs/fs-writeback.c was
   dropped).
 - Use kcalloc() instead of percpu_alloc() to allocate the dlock list
   heads structure as suggested by Christoph Lameter.
 - Replaced patch 5 by another one that made sibling CPUs use the same
   dlock list head thus reducing the number of list heads that needed
   to be maintained.

v3->v4:
 - As suggested by Al, encapsulate the dlock list mechanism into
   the dlist_for_each_entry() and dlist_for_each_entry_safe()
   which are the equivalent of list_for_each_entry() and
   list_for_each_entry_safe() for regular linked list. That simplifies
   the changes in the call sites that perform dlock list iterations.
 - Add a new patch to make the percpu head structure cacheline aligned
   to prevent cacheline contention from disrupting the performance
   of nearby percpu variables.

v2->v3:
 - Remove the 2 persubnode API patches.
 - Merge __percpu tag patch 2 into patch 1.
 - As suggested by Tejun Heo, restructure the dlock_list_head data
   structure to hide the __percpu tag and rename some of the functions
   and structures.
 - Move most of the code from dlock_list.h to dlock_list.c and export
   the symbols.

v1->v2:
 - Add a set of simple per-subnode APIs that is between percpu and
   per-node in granularity.
 - Make dlock list to use the per-subnode APIs so as to reduce the
   total number of separate linked list that needs to be managed
   and iterated.
 - There is no change in patches 1-5.

This patchset provides new APIs for a set of distributed locked lists
(one/CPU core) to minimize lock and cacheline contention. Insertion
and deletion to the list will be cheap and relatively contention free.
Lookup, on the other hand, may be a bit more costly as there are
multiple lists to iterate. This is not really a problem for the
replacement of superblock's inode list by dlock list included in
the patchset as lookup isn't needed.

For use cases that need to do lookup, the dlock list can also be
treated as a set of hashed lists that scales with the number of CPU
cores in the system.

Both patches 5 and 6 are added to support other use cases like epoll
nested callbacks, for example, which could use the dlock-list to
reduce lock contention problem.

Patch 1 introduces the dlock list. The list heads are allocated
by kcalloc() instead of percpu_alloc(). Each list head entry is
cacheline aligned to minimize contention.

Patch 2 replaces the use of list_for_each_entry_safe() in
evict_inodes() and invalidate_inodes() by list_for_each_entry().

Patch 3 modifies the superblock and inode structures to use the dlock
list. The corresponding functions that reference those structures
are modified.

Patch 4 makes the sibling CPUs use the same dlock list head to reduce
the number of list heads that need to be iterated.

Patch 5 enables alternative use case of as a set of hashed lists.

Patch 6 provides an irq safe mode specified at dlock-list allocation
time so that it can be used within interrupt context.

Jan Kara (1):
  vfs: Remove unnecessary list_for_each_entry_safe() variants

Waiman Long (5):
  lib/dlock-list: Distributed and lock-protected lists
  vfs: Use dlock list for superblock's inode list
  lib/dlock-list: Make sibling CPUs share the same linked list
  lib/dlock-list: Enable faster lookup with hashing
  lib/dlock-list: Add an IRQ-safe mode to be used in interrupt handler

 fs/block_dev.c             |   9 +-
 fs/drop_caches.c           |   9 +-
 fs/inode.c                 |  38 ++----
 fs/notify/fsnotify.c       |   9 +-
 fs/quota/dquot.c           |  14 +-
 fs/super.c                 |   7 +-
 include/linux/dlock-list.h | 263 +++++++++++++++++++++++++++++++++++
 include/linux/fs.h         |   8 +-
 lib/Makefile               |   2 +-
 lib/dlock-list.c           | 333 +++++++++++++++++++++++++++++++++++++++++++++
 10 files changed, 638 insertions(+), 54 deletions(-)
 create mode 100644 include/linux/dlock-list.h
 create mode 100644 lib/dlock-list.c

-- 
1.8.3.1