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Date: Sat, 8 May 2004 23:45:29 +0100
From: Russell King <rmk+lkml@arm.linux.org.uk>
To: Hugh Dickins <hugh@veritas.com>
Cc: Christoph Hellwig <hch@infradead.org>, Andrew Morton <akpm@osdl.org>,
       Andrea Arcangeli <andrea@suse.de>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] rmap 24 pte_young first
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In-Reply-To: <Pine.LNX.4.44.0405082332590.26651-100000@localhost.localdomain>; from hugh@veritas.com on Sat, May 08, 2004 at 11:39:32PM +0100
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On Sat, May 08, 2004 at 11:39:32PM +0100, Hugh Dickins wrote:
> rmap 25 of course
> 
> On Sat, 8 May 2004, Christoph Hellwig wrote:
> > On Sat, May 08, 2004 at 10:56:26PM +0100, Hugh Dickins wrote:
> > >  
> > > -	if (ptep_test_and_clear_young(pte))
> > > +	if (pte_young(*pte) && ptep_test_and_clear_young(pte))
> > 
> > stupid question - shouldn't the pte_young check simply move to
> > the beginning of ptep_test_and_clear_young?
> 
> I don't think that would be a good idea.  We're used to those
> test_and_clear operations being atomic, putting an initial non-atomic
> test inside would make it fundamentally non-atomic.  We know here that
> it's not the end of the world if we miss a racing transition of the
> young bit, but it wouldn't be good to hide and force that on others.

EAGAIN.

include/asm-generic/pgtable.h:

#ifndef __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
static inline int ptep_test_and_clear_young(pte_t *ptep)
{
        pte_t pte = *ptep;
        if (!pte_young(pte))
                return 0;
        set_pte(ptep, pte_mkold(pte));
        return 1;
}
#endif


-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 PCMCIA      - http://pcmcia.arm.linux.org.uk/
                 2.6 Serial core