linux-kernel - Re: virtual cache, TLB, and OS

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Message-ID: <457B97EA.3080609@goop.org>
Date:	Sat, 09 Dec 2006 21:15:22 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	xu feng <xu_feng_xu@...oo.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: virtual cache, TLB, and OS

xu feng wrote:
> I am just confused about the author:
> 1- first point, why the cache has to be bothered by
> the change in the address logical-physical mapping
> since it is a virtual cache??
>   

If you:

   1. mmap file A at virtual address X
   2. use memory at X
   3. mmap file B at X
   4. look at X

If its a virtual cache, and it wasn't flushed at step 3, then step 4
will see A's contents rather than B's.

> 2- could you please give me a situation where two
> virtual addresses from the same process are mapped to
> the same physical address? 
>
> i can't see this happening since each process page is
> allocated a dedicated frame. 
>   

If you mmap a file multiple times, then the kernel will assign multiple
different virtual addresses for the same page cache page(s).


    J
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