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Date:   Wed, 29 Nov 2017 07:26:02 -0800
From:   Davidlohr Bueso <>
To:     Waiman Long <>
Cc:     Alexander Viro <>, Jan Kara <>,
        Jeff Layton <>,
        "J. Bruce Fields" <>,
        Tejun Heo <>,
        Christoph Lameter <>,,,
        Ingo Molnar <>,
        Peter Zijlstra <>,
        Andi Kleen <>,
        Dave Chinner <>,
        Boqun Feng <>
Subject: Re: [PATCH v8 0/6] vfs: Use dlock list for SB's s_inodes list

Are you planning on sending a v9 with the discussed changes? afaict:

- Drop last two patches
- Fix tearing (WRITE/READ_ONCE())
- Reduce barrier usage for dlock_lists_empty() -- which I'll be sending
  you shortly.


On Tue, 31 Oct 2017, Waiman Long wrote:

> - 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.
> - Fix outdated email address.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.
> - 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.
> - 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.
> - 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.
> - 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.
> - 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

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