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From: Mathieu Desnoyers <>
To: "Paul E. McKenney" <>
Subject: Kernel RCU: shrink the size of the struct rcu_head
Date: Sun, 18 Oct 2009 19:29:18 -0400
Message-ID: <20091018232918.GA7385@Krystal> (raw)

Hi Paul,

I noticed that you already discussed the possibility of shrinking the
struct rcu_head by removing the function pointer.

The ideas brought in so far require having per-callback lists, which
involves a bit of management overhead and don't permit keeping the
call_rcu() in cpu order.

You might want to look into the Userspace RCU urcu-defer.c
implementation, where I perform pointer encoding to compact the usual
case, expected to be the same callback passed as parameter multiple
times in a row to call_rcu(). This is very typical with multiple free()
calls for different data structures next to each other.

This typically keeps the size of the information to encode per callback
down to a minimum: the size of a single pointer. It would be good to
trace the kernel usage of call_rcu() to see if my assumption holds.

I just thought I should tell you before you start looking at this
issue further.



Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

             reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-10-18 23:29 Mathieu Desnoyers [this message]
2009-10-20 22:07 ` Paul E. McKenney
2009-10-21 14:53   ` Mathieu Desnoyers
2009-10-23  0:40     ` Paul E. McKenney
2009-10-23 12:29       ` Mathieu Desnoyers
2009-10-23 16:22         ` Paul E. McKenney
2009-10-23 17:41           ` Mathieu Desnoyers

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