Here is updated one, thanks again. --- From: Cyrill Gorcunov <gorcunov@xxxxxxxxx> Subject: [PATCH] docs: Document soft dirty behaviour for freshly created memory regions Signed-off-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx> Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Matt Mackall <mpm@xxxxxxxxxxx> Cc: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx> Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxx> Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> --- 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 lose soft dirty bits -- a task +unmaps a previously mapped memory region and then maps a new one at exactly +the same place. When unmap is called, the kernel internally clears PTE values +including soft dirty bits. To notify user space application about such +memory region renewal the kernel always marks new memory regions (and +expanded regions) as soft dirty. 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@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>