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Re: [PATCH v4 0/5] vfs: Use dlock list for SB's s_inodes list

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Hello, Christoph.

On Mon, Jul 25, 2016 at 08:48:25AM -0500, Christoph Lameter wrote:
> On Fri, 22 Jul 2016, Waiman Long wrote:
> 
> >  - Add a new patch to make the percpu head structure cacheline aligned
> >    to prevent cacheline contention from disrupting the performance
> >    of nearby percpu variables.
> 
> It would be better not to use the percpu allocation etc for this.
> Given the frequency of off node data access I would say that the data
> structure does not qualify as per cpu data. You have per cpu data items
> yes but this is not used as per cpu data.

I don't get it.  What's the harm of using percpu memory here?  Other
percpu data structures have remote access too.  They're to a lower
degree but I don't see a clear demarcation line and making addtions
per-cpu seems to have significant benefits here.  If there's a better
way of splitting the list and locking, sure, let's try that but short
of that I don't see anything wrong with doing this per-cpu.

Thanks.

-- 
tejun

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[PATCH v4 0/5] vfs: Use dlock list for SB's s_inodes list Waiman Long <Waiman.Long@hpe.com> - 2016-07-22 22:40 +0200
  [PATCH v4 4/5] vfs: Use dlock list for superblock's inode list Waiman Long <Waiman.Long@hpe.com> - 2016-07-22 22:40 +0200
  [PATCH v4 2/5] fsnotify: Simplify inode iteration on umount Waiman Long <Waiman.Long@hpe.com> - 2016-07-22 22:40 +0200
  [PATCH v4 1/5] lib/dlock-list: Distributed and lock-protected lists Waiman Long <Waiman.Long@hpe.com> - 2016-07-22 22:40 +0200
  [PATCH v4 3/5] vfs: Remove unnecessary list_for_each_entry_safe() variants Waiman Long <Waiman.Long@hpe.com> - 2016-07-22 22:40 +0200
  Re: [PATCH v4 0/5] vfs: Use dlock list for SB's s_inodes list Christoph Lameter <cl@linux.com> - 2016-07-25 15:50 +0200
    Re: [PATCH v4 0/5] vfs: Use dlock list for SB's s_inodes list Tejun Heo <tj@kernel.org> - 2016-07-25 19:50 +0200
      Re: [PATCH v4 0/5] vfs: Use dlock list for SB's s_inodes list Christoph Lameter <cl@linux.com> - 2016-07-27 17:20 +0200

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