Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1331360

Re: Another proposal for DAX fault locking

Show all headers | View raw

On 02/09/2016 07:24 PM, Jan Kara wrote:
> Hello,
> 
> I was thinking about current issues with DAX fault locking [1] (data
> corruption due to racing faults allocating blocks) and also races which
> currently don't allow us to clear dirty tags in the radix tree due to races
> between faults and cache flushing [2]. Both of these exist because we don't
> have an equivalent of page lock available for DAX. While we have a
> reasonable solution available for problem [1], so far I'm not aware of a
> decent solution for [2]. After briefly discussing the issue with Mel he had
> a bright idea that we could used hashed locks to deal with [2] (and I think
> we can solve [1] with them as well). So my proposal looks as follows:
> 
> DAX will have an array of mutexes (the array can be made per device but
> initially a global one should be OK). We will use mutexes in the array as a
> replacement for page lock - we will use hashfn(mapping, index) to get
> particular mutex protecting our offset in the mapping. On fault / page
> mkwrite, we'll grab the mutex similarly to page lock and release it once we
> are done updating page tables. This deals with races in [1]. When flushing
> caches we grab the mutex before clearing writeable bit in page tables
> and clearing dirty bit in the radix tree and drop it after we have flushed
> caches for the pfn. This deals with races in [2].
> 
> Thoughts?
> 

You could also use one of the radix-tree's special-bits as a bit lock.
So no need for any extra allocations.

[latest page-lock is a bit-lock so performance is the same]

Thanks
Boaz

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Another proposal for DAX fault locking Jan Kara <jack@suse.cz> - 2016-02-09 18:30 +0100
  Re: Another proposal for DAX fault locking Dan Williams <dan.j.williams@intel.com> - 2016-02-09 19:20 +0100
    Re: Another proposal for DAX fault locking Jan Kara <jack@suse.cz> - 2016-02-10 11:40 +0100
      Re: Another proposal for DAX fault locking Dan Williams <dan.j.williams@intel.com> - 2016-02-10 21:10 +0100
        Re: Another proposal for DAX fault locking Jan Kara <jack@suse.cz> - 2016-02-11 11:50 +0100
      Re: Another proposal for DAX fault locking Dave Chinner <david@fromorbit.com> - 2016-02-10 23:20 +0100
        Re: Another proposal for DAX fault locking Cedric Blancher <cedric.blancher@gmail.com> - 2016-02-10 23:40 +0100
          Re: Another proposal for DAX fault locking Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-02-11 00:40 +0100
          Re: Another proposal for DAX fault locking Jan Kara <jack@suse.cz> - 2016-02-11 12:00 +0100
            Re: Another proposal for DAX fault locking Cedric Blancher <cedric.blancher@gmail.com> - 2016-02-11 22:10 +0100
        Re: Another proposal for DAX fault locking Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-02-11 00:40 +0100
          Re: Another proposal for DAX fault locking Jan Kara <jack@suse.cz> - 2016-02-11 12:20 +0100
  Re: Another proposal for DAX fault locking Cedric Blancher <cedric.blancher@gmail.com> - 2016-02-09 19:50 +0100
    Re: Another proposal for DAX fault locking Mel Gorman <mgorman@suse.de> - 2016-02-10 09:20 +0100
      Re: Another proposal for DAX fault locking Jan Kara <jack@suse.cz> - 2016-02-10 11:20 +0100
  Re: Another proposal for DAX fault locking Dmitry Monakhov <dmonlist@gmail.com> - 2016-02-10 13:40 +0100
    Re: Another proposal for DAX fault locking Jan Kara <jack@suse.cz> - 2016-02-10 13:40 +0100
  Re: Another proposal for DAX fault locking Boaz Harrosh <boaz@plexistor.com> - 2016-02-10 18:40 +0100
    Re: Another proposal for DAX fault locking Jan Kara <jack@suse.cz> - 2016-02-11 11:40 +0100
      Re: Another proposal for DAX fault locking Boaz Harrosh <openosd@gmail.com> - 2016-02-14 10:00 +0100
  Re: Another proposal for DAX fault locking Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-02-11 00:50 +0100
    Re: Another proposal for DAX fault locking Cedric Blancher <cedric.blancher@gmail.com> - 2016-02-11 01:00 +0100
      Re: Another proposal for DAX fault locking Ross Zwisler <ross.zwisler@linux.intel.com> - 2016-02-11 01:20 +0100

csiph-web