On Wed, May 08, 2019 at 11:16:38AM -0700, Paul E. McKenney wrote:
[snip]

quoted

The other example could be dentry look up which uses seqlocks for the
RCU-walk case? But that could be too complex. This is also something I first
learnt from the paper and then the excellent path-lookup.rst document in
kernel sources.

This is a great example, but it would need serious simplification for
use in the Documentation/RCU directory.  Note that dcache uses it to
gain very limited and targeted consistency -- only a few types of updates
acquire the write-side of that seqlock.

Might be quite worthwhile to have a simplified example, though!
Perhaps a trivial hash table where write-side sequence lock is acquired
only when moving an element from one chain to another?

Here you meant "moving from one chain to another" in the case of
hashtable-resizing right? I could not think of another reason why an element
is moved between 2 hash chains.

I just finished reading the main parts of Josh's relativistic hashtable paper
[1] and it is very cool indeed. The whole wait-for-readers application for
hashtable expansion is so well thought. I am planning to go over more papers
and code and can certainly update this example with a read-mostly hashtable
example as well as you are suggesting. :-)

[1] https://www.usenix.org/legacy/event/atc11/tech/final_files/Triplett.pdf

thanks,

 - Joel