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List:       linux-arm-kernel
Subject:    Re: On TLB flushing
From:       Russell King - ARM Linux <linux () arm ! linux ! org ! uk>
Date:       2004-04-20 16:43:50
Message-ID: 20040420174350.H16499 () flint ! arm ! linux ! org ! uk
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On Tue, Apr 20, 2004 at 09:34:37AM -0700, Marc Singer wrote:
> On Tue, Apr 20, 2004 at 05:01:43PM +0100, Russell King - ARM Linux wrote:
> > On Fri, Apr 16, 2004 at 09:18:45PM +0200, Matthias Welwarsky wrote:
> > > Yes, but if the young bit is not refreshed, mapped pages that are not involved 
> > > in file IO are inevitably discarded. If they're read-only, they will never 
> > > again become "young" unless they're paged back in from disk.
> > 
> > Ok.  2.6 is more agressive than 2.4 with respect to the page age
> > state, which means we should flush the TLB when we clear the young
> > bit.
> > 
> 
> Have you found a case that shows that flushing the TLB when we clear
> the YOUNG bit is necessary?

The action of the 2.6 MM is now to delay checking the young bits until
the very last moment, just before the page is thrown out.  In 2.4,
there was a grace period because of the way the page cache and page
scanning worked.

This means that to stop pages being unnecessarily thrown out, the
young bit needs to be known more precisely than with 2.4.

There are also rumours that some updates to the MM which are just
around the corner will be more critical on the behaviour of the
page age, requiring it to be less of a mere hint.

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