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Date: Thu, 12 Apr 2007 16:12:42 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Nick Piggin <nickpiggin@yahoo.com.au>
CC: Eric Dumazet <dada1@cosmosbay.com>, Rik van Riel <riel@redhat.com>,
       linux-kernel <linux-kernel@vger.kernel.org>,
       linux-mm <linux-mm@kvack.org>, Ulrich Drepper <drepper@redhat.com>
Subject: Re: [PATCH] make MADV_FREE lazily free memory
References: <461C6452.1000706@redhat.com> <461D6413.6050605@cosmosbay.com> <461D67A9.5020509@redhat.com> <461DC75B.8040200@cosmosbay.com> <461DCCEB.70004@yahoo.com.au>
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Nick Piggin wrote:
> Eric Dumazet wrote:
> 

>>> Two things can happen here.
>>>
>>> If this program used the pages before the kernel needed
>>> them, the program will be reusing its old pages.
>>
>>
>>
>> ah ok, this is because accessed/dirty bits are set by hardware and not 
>> a page fault.
> 
> 
> No it isn't.

That is to say, it isn't required for correctness. But if the
question was about avoiding a fault, then yes ;)

But as Linus recently said, even hardware handled faults still
take expensive microarchitectural traps.

> 
>> Is it true for all architectures ?
> 
> 
> No.
> 


-- 
SUSE Labs, Novell Inc.