From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx166.postini.com [74.125.245.166]) by kanga.kvack.org (Postfix) with SMTP id EFB946B0036 for ; Tue, 20 Aug 2013 11:31:35 -0400 (EDT) Received: by mail-la0-f48.google.com with SMTP id er20so429171lab.21 for ; Tue, 20 Aug 2013 08:31:34 -0700 (PDT) Date: Tue, 20 Aug 2013 19:31:32 +0400 From: Cyrill Gorcunov Subject: [PATCH -mm] docs: Document soft dirty behaviour for freshly created memory regions Message-ID: <20130820153132.GK18673@moon> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andy Lutomirski , Pavel Emelyanov , Matt Mackall , Xiao Guangrong , Marcelo Tosatti , KOSAKI Motohiro , Stephen Rothwell , Peter Zijlstra , "Aneesh Kumar K.V" Signed-off-by: Cyrill Gorcunov Cc: Pavel Emelyanov Cc: Andy Lutomirski Cc: Andrew Morton Cc: Matt Mackall Cc: Xiao Guangrong Cc: Marcelo Tosatti Cc: KOSAKI Motohiro Cc: Stephen Rothwell Cc: Peter Zijlstra Cc: "Aneesh Kumar K.V" --- Documentation/vm/soft-dirty.txt | 7 +++++++ 1 file changed, 7 insertions(+) Index: linux-2.6.git/Documentation/vm/soft-dirty.txt =================================================================== --- linux-2.6.git.orig/Documentation/vm/soft-dirty.txt +++ linux-2.6.git/Documentation/vm/soft-dirty.txt @@ -28,6 +28,13 @@ This is so, since the pages are still ma the kernel does is finds this fact out and puts both writable and soft-dirty bits on the PTE. + While in most cases tracking memory changes by #PF-s is more than enough +there is still a scenario when we can loose soft dirty bit -- a task does +unmap previously mapped memory region and then maps new one exactly at the +same place. When unmap called the kernel internally clears PTEs values +including soft dirty bit. To notify user space application about such +memory region renewal the kernel always mark new memory regions (and +expanded regions) as soft dirtified. This feature is actively used by the checkpoint-restore project. You can find more details about it on http://criu.org -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org