Re: Is there a reason we don't have kvfree_rcu()?

[Uladzislau Rezki <urezki@gmail.com>]

On Fri, Mar 13, 2020 at 05:06:59AM +0000, George Spelvin wrote:
> I'd just like to mention that the is_vmalloc_addr() test depends only on 
> the virtual address, so can be done when the memory is queued, before the 
> grace period.  That is, you could have kfree_rcu(), vfree_rcu(), and a 
> kvfree_rcu() function which decides between them.
> 
> One advantage of that would be that you could put the vfree() sanity
> checks into vfree_rcu(), so errors would have a useful backtrace,
> and just do the __vunmap when the grace period expires.
> 
> Or you could build a mixed queue and do the is_vmalloc_addr() test at
> the end of the grace period.  That was my original idea, because it
> avoids the need for a separate queue.  (In the _rcu_bulk_data structure,
> you can do a quicksort-style partitioning on is_vmalloc_addr(), so
> the kfree_bulk() pointers are all contiguous.)
> 
> Just an implementation option.
Thanks for your input. Mixed queue would require sorting, one node can
contain up to ~509 elements if PAGE_SIZE is 4096, so i am not sure how
it would impact performance under heavy load. But anyway, thanks again.

--
Vlad Rezki