[lustre-devel] Lustre use of hash_long() & cfs_hash_u32_hash()

[James Simmons]

> Thank you very much for the response!
> 
> > Thanks for looking into this. Do you have a tree some where we can look
> > at for the changes?
> 
> Linus committed the most important fix to 4.6-rc7 as
> 689de1d6ca95b3b5bd8ee446863bf81a4883ea25

Not too huge of a changed. Looks like I need to move to using these 
functions.

> I'm following up with additional, less urgent cleanups of kernel hashing.
> 
> (Fundamentally, I'm trying to reduce the number of different hash
> functions, and find a good balance between execution-time performance
> and mixing performance of what remains.)

Looking at our code I see our duplication is cfs_hash_u32_hash and
cfs_hash_u64_hash which could be replaced by the standard linux functions.
Am I missing anything else?

> > Details about this change are at
> > 
> > https://jira.hpdd.intel.com/browse/LU-143
> > 
> > and the original patch with those changes are at
> > 
> > http://review.whamcloud.com/#/c/374
> 
> Thanks a lot for the pointers!

Any time. I also CC Liang Zhen who wrote the bulk of the hashing code.

> > Is this the only code that doesn't make sense or is their more?
> 
> I expect there's more; that was just what first jumped out at me.
> My primary goal was elsewhere, so once it became clear that Lustre would
> be a time-consuming side quest, I gave up and sent that e-mail.
> 
> But if Lustre would appreciate more attention, I can take another look.

Yep. We are here to help. 

> I did do a pass over the kernel and fixed improper use of the current
> <linux/hash.h> functions.  I posted it as
> 
> Subject: [RFC PATCH 3/2] (Rant) Fix various hash abuses
> https://marc.info/?l=linux-kernel&m=146218484201133
> 
> Since Lustre was the single biggest culprit (about 25% of that patch),
> I was planning on sending a broken-out patch.

I expect this is not all the changes needed. Do you have a newer patch or 
should I run with this patch? Also I will look into replace the 
cfs_hash_u[32|64]_* code with standard linux hash code.