[lustre-devel] Lustre interval tree problems

NeilBrown neilb at suse.com
Wed Feb 20 14:37:58 PST 2019


On Wed, Feb 20 2019, James Simmons wrote:

> With the port of the interval tree work to the OpenSFS branch several 
> problems have been pointed out in the implementation which impacts
> performance and the memory footprint in some cases.
>
> The biggest issues is the ability to add duplicate locks. The reason
> the original implementation avoided adding duplicate locks was to
> avoid the extra compares being done with the same type of locks.
> Especially in the case of the range lock where you can end up with
> many duplicate read locks [0-EOF]. Comparing with 1000s of identical
> read locks will have an impact. Their is teh question of the memory
> foot print in this case as well. I believe this is the case with the
> ldlm locks as well since the ability to skip large lock amounts if
> not matching has been lost.
>
> The next problem Vitaly pointed in the implementation is the emebedding
> of lit_root in ldlm_interval_tree also has a negative impact. Since many
> locaks are kept in memory he wants to see that ldlm_lock struct stay as
> small as possible. Explained that is why ldlm_interval was not original
> embedded but allocated separately. I added him to this chain.

Thanks for this valuable feedback!  I'll look over the code again with
these issues in mind, and let you know what I find.

NeilBrown
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