linux-kernel - Re: [PATCH v1 2/6] rcu: introduce kvfree

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Date:   Mon, 16 Mar 2020 14:57:18 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Uladzislau Rezki <urezki@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        RCU <rcu@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: Re: [PATCH v1 2/6] rcu: introduce kvfree_rcu() interface

On Mon, Mar 16, 2020 at 2:55 PM Uladzislau Rezki <urezki@...il.com> wrote:
>
> On Mon, Mar 16, 2020 at 11:45:39AM -0400, Joel Fernandes wrote:
> > On Sun, Mar 15, 2020 at 07:18:36PM +0100, Uladzislau Rezki (Sony) wrote:
> > > kvfree_rcu() can deal with an allocated memory that is obtained
> > > via kvmalloc(). It can return two types of allocated memory or
> > > "pointers", one can belong to regular SLAB allocator and another
> > > one can be vmalloc one. It depends on requested size and memory
> > > pressure.
> > >
> > > Based on that, two streams are split, thus if a pointer belongs
> > > to vmalloc allocator it is queued to the list, otherwise SLAB
> > > one is queued into "bulk array" for further processing.
> > >
> > > The main reason of such splitting is:
> > >     a) to distinguish kmalloc()/vmalloc() ptrs;
> > >     b) there is no vmalloc_bulk() interface.
> > >
> > > As of now we have list_lru.c user that needs such interface,
> > > also there will be new comers. Apart of that it is preparation
> > > to have a head-less variant later.
> > >
> > > Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> > > ---
> > >  include/linux/rcupdate.h |  9 +++++++++
> > >  kernel/rcu/tiny.c        |  3 ++-
> > >  kernel/rcu/tree.c        | 17 ++++++++++++-----
> > >  3 files changed, 23 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > > index 2be97a83f266..bb270221dbdc 100644
> > > --- a/include/linux/rcupdate.h
> > > +++ b/include/linux/rcupdate.h
> > > @@ -845,6 +845,15 @@ do {                                                                   \
> > >             __kfree_rcu(&((___p)->rhf), offsetof(typeof(*(ptr)), rhf)); \
> > >  } while (0)
> > >
> > > +/**
> > > + * kvfree_rcu() - kvfree an object after a grace period.
> > > + * @ptr:   pointer to kvfree
> > > + * @rhf:   the name of the struct rcu_head within the type of @ptr.
> > > + *
> > > + * Same as kfree_rcu(), just simple alias.
> > > + */
> > > +#define kvfree_rcu(ptr, rhf) kfree_rcu(ptr, rhf)
> > > +
> > >  /*
> > >   * Place this after a lock-acquisition primitive to guarantee that
> > >   * an UNLOCK+LOCK pair acts as a full barrier.  This guarantee applies
> > > diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
> > > index dd572ce7c747..4b99f7b88bee 100644
> > > --- a/kernel/rcu/tiny.c
> > > +++ b/kernel/rcu/tiny.c
> > > @@ -23,6 +23,7 @@
> > >  #include <linux/cpu.h>
> > >  #include <linux/prefetch.h>
> > >  #include <linux/slab.h>
> > > +#include <linux/mm.h>
> > >
> > >  #include "rcu.h"
> > >
> > > @@ -86,7 +87,7 @@ static inline bool rcu_reclaim_tiny(struct rcu_head *head)
> > >     rcu_lock_acquire(&rcu_callback_map);
> > >     if (__is_kfree_rcu_offset(offset)) {
> > >             trace_rcu_invoke_kfree_callback("", head, offset);
> > > -           kfree((void *)head - offset);
> > > +           kvfree((void *)head - offset);
> > >             rcu_lock_release(&rcu_callback_map);
> > >             return true;
> > >     }
> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > index 2f4c91a3713a..1c0a73616872 100644
> > > --- a/kernel/rcu/tree.c
> > > +++ b/kernel/rcu/tree.c
> > > @@ -2899,9 +2899,9 @@ static void kfree_rcu_work(struct work_struct *work)
> > >     }
> > >
> > >     /*
> > > -    * Emergency case only. It can happen under low memory
> > > -    * condition when an allocation gets failed, so the "bulk"
> > > -    * path can not be temporary maintained.
> > > +    * vmalloc() pointers end up here also emergency case. It can
> >
> > Suggest rephrase for clarity:
> >
> > nit: We can end up here either with 1) vmalloc() pointers or 2) low on memory
> > and could not allocate a bulk array.
> >
> Let's go with your suggestion. I see that you took patches to your tree.
> Could you please update it on your own? Otherwise i can send out V2, so
> please let me know.

I updated it, "patch -p1" resolved the issue. No need to resend unless
something in my tree looks odd to you :)

> Thanks for the comments!

Thanks!

- Joel