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From:   Uladzislau Rezki <urezki@gmail.com>
Date:   Mon, 16 Mar 2020 19:55:19 +0100
To:     Joel Fernandes <joel@joelfernandes.org>
Cc:     "Uladzislau Rezki (Sony)" <urezki@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        RCU <rcu@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Subject: Re: [PATCH v1 2/6] rcu: introduce kvfree_rcu() interface
Message-ID: <20200316185519.GA10577@pc636>
References: <20200315181840.6966-1-urezki@gmail.com>
 <20200315181840.6966-3-urezki@gmail.com>
 <20200316154539.GE190951@google.com>
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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@gmail.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.

Thanks for the comments!

--
Vlad Rezki