From: Uladzislau Rezki <urezki@gmail.com>
To: "Paul E. McKenney" <paulmck@kernel.org>,
"joel@joelfernandes.org George Spelvin" <lkml@sdf.org>
Cc: George Spelvin <lkml@SDF.ORG>,
rcu@vger.kernel.org, josh@joshtriplett.org, rostedt@goodmis.org,
mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
joel@joelfernandes.org, urezki@gmail.com
Subject: Re: Is there a reason we don't have kvfree_rcu()?
Date: Thu, 12 Mar 2020 20:10:09 +0100 [thread overview]
Message-ID: <20200312191009.GA27429@pc636> (raw)
In-Reply-To: <20200312181138.GI3199@paulmck-ThinkPad-P72>
On Thu, Mar 12, 2020 at 11:11:38AM -0700, Paul E. McKenney wrote:
> On Thu, Mar 12, 2020 at 04:27:30PM +0000, George Spelvin wrote:
> > kvfree() is a superset of kfree(), so there's nothing obvious stopping
> > kfree_rcu() from simply changing to kvfree() and everything will keep
> > working.
> >
> > I'd probably add a kvfree_rcu() alias, just for documentation's sake and
> > to make code that depends on the new feature explode at compile time, but
> > it could be identical behind the scenes.
> >
> > There's an existing user in mm/list_lru.c already.
> >
> > I was just thinking of using kvmalloc() in a module, and realized that the
> > lack of a core kvfree_rcu() helper meant I'd have to synchronize_rcu() on
> > module unload.
>
> There was a recent proposal to do just that, but current patches in -rcu
> use kfree_bulk(). It doesn't look to me that this works for kfvree()
> under the covers in its current form. Could it be upgraded to handle
> this case?
>
> Adding Vlad on CC for his thoughts.
>
Paul, see below my view:
Answering to topic's question it looks like we need kvfree_rcu() support :)
It is easy to add it actually. But if we are talking about the case when
an object has rcu_head inside. From the other hand recent discussion showed
that we would like to have head-less variant of the kvfree_rcu() functionality:
https://lkml.org/lkml/2020/2/18/566
for example, as Ted pointed, he would go with head-less case(for ext4) only.
The reason is nobody wants to modify internal structures injecting rcu_head
there. Also there are many other places in the kernel where it would be good
to have kfree_rcu() head-less variant as well.
I spent some time implementing it together with Joel. It is ready from my
side but only for RCU-tree case. Next step is RCU-tiny support, so i am
working on it.
I can send out an RFC for RCU-tree only support, so we can discuss it
and agree on how to move forward. After that i or Joel or together can
update RCU-tine.
Joel: What do you think?
Another thought. We can add kvfree_rcu(ptr, rcu) first, because it is
easy and after that implement head-less case.
--
Vlad Rezki
next prev parent reply other threads:[~2020-03-12 19:10 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-12 16:27 Is there a reason we don't have kvfree_rcu()? George Spelvin
2020-03-12 18:11 ` Paul E. McKenney
2020-03-12 19:10 ` Uladzislau Rezki [this message]
2020-03-13 3:58 ` Joel Fernandes
2020-03-13 13:21 ` Uladzislau Rezki
2020-03-13 13:40 ` Joel Fernandes
2020-03-13 5:06 ` George Spelvin
2020-03-13 13:44 ` Uladzislau Rezki
2020-03-13 13:54 ` Paul E. McKenney
2020-03-13 16:52 ` George Spelvin
2020-03-13 18:19 ` Paul E. McKenney
2020-03-13 18:46 ` George Spelvin
2020-03-13 19:58 ` Paul E. McKenney
2020-03-12 22:24 ` George Spelvin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200312191009.GA27429@pc636 \
--to=urezki@gmail.com \
--cc=jiangshanlai@gmail.com \
--cc=joel@joelfernandes.org \
--cc=josh@joshtriplett.org \
--cc=lkml@sdf.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=paulmck@kernel.org \
--cc=rcu@vger.kernel.org \
--cc=rostedt@goodmis.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).