linux-kernel - Re: [PATCH 0/2] rcu: Transform kfree_rcu() into kvfree

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Message-Id: <20180207082029.GJ3617@linux.vnet.ibm.com>
Date:   Wed, 7 Feb 2018 00:20:29 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Josh Triplett <josh@...htriplett.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>, rostedt@...dmis.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        mingo@...hat.com, cl@...ux.com, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, brouer@...hat.com, rao.shoaib@...cle.com
Subject: Re: [PATCH 0/2] rcu: Transform kfree_rcu() into kvfree_rcu()

On Tue, Feb 06, 2018 at 11:54:09PM -0800, Josh Triplett wrote:
> On Tue, Feb 06, 2018 at 09:02:00PM -0800, Paul E. McKenney wrote:
> > On Tue, Feb 06, 2018 at 08:23:34PM -0800, Matthew Wilcox wrote:
> > > On Tue, Feb 06, 2018 at 06:17:03PM -0800, Paul E. McKenney wrote:
> > > > So it is OK to kvmalloc() something and pass it to either kfree() or
> > > > kvfree(), and it had better be OK to kvmalloc() something and pass it
> > > > to kvfree().
> > > > 
> > > > Is it OK to kmalloc() something and pass it to kvfree()?
> > > 
> > > Yes, it absolutely is.
> > > 
> > > void kvfree(const void *addr)
> > > {
> > >         if (is_vmalloc_addr(addr))
> > >                 vfree(addr);
> > >         else
> > >                 kfree(addr);
> > > }
> > > 
> > > > If so, is it really useful to have two different names here, that is,
> > > > both kfree_rcu() and kvfree_rcu()?
> > > 
> > > I think it's handy to have all three of kvfree_rcu(), kfree_rcu() and
> > > vfree_rcu() available in the API for the symmetry of calling kmalloc()
> > > / kfree_rcu().
> > > 
> > > Personally, I would like us to rename kvfree() to just free(), and have
> > > malloc(x) be an alias to kvmalloc(x, GFP_KERNEL), but I haven't won that
> > > fight yet.
> > 
> > But why not just have the existing kfree_rcu() API cover both kmalloc()
> > and kvmalloc()?  Perhaps I am not in the right forums, but I am not hearing
> > anyone arguing that the RCU API has too few members.  ;-)
> 
> I don't have any problem with having just `kvfree_rcu`, but having just
> `kfree_rcu` seems confusingly asymmetric.

I don't understand why kmalloc()/kvfree_rcu() would seem any less
asymmetric than kvmalloc()/kfree_rcu().

> (Also, count me in favor of having just one "free" function, too.)

We agree on that much, anyway.  ;-)

							Thanx, Paul