Messages in this thread | | | Subject | Re: [PATCH v2 6/9] mm: free user PTE page table pages | From | Qi Zheng <> | Date | Thu, 2 Sep 2021 14:53:58 +0800 |
| |
On 2021/9/1 PM11:32, Jason Gunthorpe wrote: > >>> Also, I don't really understand how this scheme works with >>> get_user_pages_fast. >> >> With the RCU change it in #8 it should work just fine, because RCU >> synchronize has to wait either until all other CPUs have left the RCU read >> section, or re-enabled interrupts. > > So at this point in the series fast gup is broken, that does mean the > series presentation really needs to be reworked. The better > presentation is to add the API changes, with a > no-functional-difference implementation, push the new API in well > split patches to all the consumption sites, then change the API to > have the new semantics. > > RCU and refcount to free the page levels seems like a reasonable > approach, but I have to say I haven't thought it through fully - are > all the contexts that have the pte deref safe to do call_rcu?
See Documentation/RCU/rcubarrier.rst:
"Since call_rcu() never blocks, this code can safely be used from within IRQ context."
So I think call_rcu() can be safely run in any context.
Thinks, Qi
> > Jason > >
| |