linux-kernel - Re: [PATCH tip/core/rcu 0/6] Preview of RCU patches for 2.6.40

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Message-ID: <20110502080906.GS2297@linux.vnet.ibm.com>
Date:	Mon, 2 May 2011 01:09:06 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Dave Chinner <david@...morbit.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, patches@...ro.org
Subject: Re: [PATCH tip/core/rcu 0/6] Preview of RCU patches for 2.6.40

On Mon, May 02, 2011 at 09:49:11AM +1000, Dave Chinner wrote:
> On Sun, May 01, 2011 at 06:21:42AM -0700, Paul E. McKenney wrote:
> > Hello!
> > 
> > This patchset introduces RCU_TREE priority boosting, a new "fire and
> > forget" kfree_rcu() API, numerous uses of kfree_rcu(), plus a number
> > of other fixes and improvements.  The patches are as follows:
> 
> .....
> 
> > 34-70.	Use kfree_rcu() throughout the kernel.  This set of patches has
> > 	Acked-by's, so will go up -tip.
> > 
> > 71-86.	Ditto, but lacking Acked-by's.
> 
> Any reason why dentry and inode freeing was not converted in this
> series?

>From what I can see, they use kmem_cache_free() rather than kfree(),
so we cannot use kfree_rcu() for them.  But there are many tens of RCU
callback functions that just do kmem_cache_free(), so maybe we need
a kmem_cache_free_rcu().

Lai, any thoughts on this?  Perhaps a global array of pointers to all the
kmem_caches, so that the low-order bit can say kmem_cache_free() rather
than kfree()?  Then the offset can be encoded in the kmem_cache structure,
allowing the ->func field of rcu_head to encode only the index of the
global array of pointers to kmem_cache structures?  Or would something
else work better?

							Thanx, Paul
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