Kernel Locking Question

[nick]

On 2015-03-11 09:48 PM, Valdis.Kletnieks at vt.edu wrote:
> On Wed, 11 Mar 2015 19:03:33 -0400, Nicholas Krause said:
> 
>> was wondering of how this would improve file system scalability and
>> reliability if implemented in file system code for btrfs worker threads.
> 
> Step 1: Figure out what locks are contended in actual systems.
> Step 2: Determine if the scope of a contended lock can be reduced.
> Step 3: ???
> Step 4: Profit!
> 
> Note that improving scalability will often cause reliability issues,
> because as you decompose locks into sets of smaller locks, you increase
> the number of ways you can get it wrong.  The BKL, for all its uglyness,
> was pretty hard to screw up.  On the other hand, we probably would never
> have gotten rid of it if somebody hadn't put lockdep into the kernel.  It
> was painful enough even with automated testing tools....
> 
Thanks Valdis,
That makes sense to me. I was wondering however about the reader vs writer issues
in file systems too as this seems to me coming up a lot in btrfs and  other file
systems for various reasons.
Thanks Nick