Messages in this thread | | | Date | Wed, 7 Feb 2018 20:09:10 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 0/2] rcu: Transform kfree_rcu() into kvfree_rcu() |
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On Wed, Feb 07, 2018 at 08:57:00AM -0500, Steven Rostedt wrote: > On Wed, 7 Feb 2018 00:31:04 -0800 > "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote: > > > I see problems. We would then have two different names for exactly the > > same thing. > > > > Seems like it would be a lot easier to simply document the existing > > kfree_rcu() behavior, especially given that it apparently already works. > > The really doesn't seem to me to be worth a name change. > > Honestly, I don't believe this is an RCU sub-system decision. This is a > memory management decision.
I couldn't agree more!
To that end, what are your thoughts on this patch?
https://lkml.kernel.org/r/1513895570-28640-1-git-send-email-rao.shoaib@oracle.com
Advantages include the ability to optimize based on sl[aou]b state, getting rid of the 4K offset hack in __is_kfree_rcu_offset(), better cache localite, and, as you say, putting the naming responsibility in the memory-management domain.
> If we have kmalloc(), vmalloc(), kfree(), vfree() and kvfree(), and we > want kmalloc() to be freed with kfree(), and vmalloc() to be freed with > vfree(), and for strange reasons, we don't know how the data was > allocated we have kvfree(). That's an mm decision not an rcu one. We > should have kfree_rcu(), vfree_rcu() and kvfree_rcu(), and honestly, > they should not depend on kvfree() doing the same thing for everything. > Each should call the corresponding member that they represent. Which > would change this patch set. > > Why? Too much coupling between RCU and MM. What if in the future > something changes and kvfree() goes away or changes drastically. We > would then have to go through all the users of RCU to change them too. > > To me kvfree() is a special case and should not be used by RCU as a > generic function. That would make RCU and MM much more coupled than > necessary.
And that is one reason I am viewing the name-change patch with great suspicion, especially given that there seems to be some controversy among the memory-management folks as to exactly what the names should be.
Thanx, Paul
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