Date: Thu, 28 Jun 2007 22:37:34 -0700 (PDT)
Message-Id: <20070628.223734.21928089.davem@davemloft.net>
To: akpm@linux-foundation.org
Cc: clameter@sgi.com, hugh@veritas.com, James.Bottomley@steeleye.com,
       rmk+lkml@arm.linux.org.uk, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Containment measures for slab objects on scatter
 gather lists
From: David Miller <davem@davemloft.net>
In-Reply-To: <20070628222424.4cbae90c.akpm@linux-foundation.org>
References: <Pine.LNX.4.64.0706282128570.11739@schroedinger.engr.sgi.com>
	<20070628.220606.112621271.davem@davemloft.net>
	<20070628222424.4cbae90c.akpm@linux-foundation.org>
Mime-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 881
Lines: 24

From: Andrew Morton <akpm@linux-foundation.org>
Date: Thu, 28 Jun 2007 22:24:24 -0700

> So what happens when two quite different threads of control are doing
> IO against two hunks of kmalloced memory which happen to come from the same
> page?  Either some (kernel-wide) locking is needed, or that pageframe needs
> to be treated as readonly?

Or you put an atomic_t at the beginning or tail of every SLAB
object.  It's a space cost not a runtime cost for the common
case which is:

	smp_rmb();
	if (atomic_read(&slab_obj->count) == 1)
		really_free_it();
	else if (atomic_dec_and_test(...))

Note I don't like this variant either. :)

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/