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Re: Why don't shared anonymous mappings work?

To: Colin Plumb <colin@nyx.net>
Subject: Re: Why don't shared anonymous mappings work?
From: ebiederm+eric@ccr.net (Eric W. Biederman)
Date: 05 Jan 1999 22:05:06 -0600
Cc: linux-mm@kvack.org
In-Reply-To: Colin Plumb's message of "Tue, 5 Jan 1999 05:51:52 -0700 (MST)"
References: <199901051251.FAA15706@nyx10.nyx.net>
Sender: owner-linux-mm@kvack.org

Take a page map it into two processes.
Swap the page out from both processes to disk.
The swap address is now in the pte's.
Bring that page into process 1.
Dirty the page, thus causing a new swap entry to be allocated.
   ( The write once rule)
Swap the page out of process 1.

Oops process 1 and process 2 have different pte's for the same
page.

Since we don't have any form of reverse page table entry
preventing that last case is difficult to do effciently.

Eric

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References:
- Why don't shared anonymous mappings work?
  - From: Colin Plumb <colin@nyx.net>

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