Merge tag 'platform-drivers-x86-v4.9-2' of git://git.infradead.org/users/dvhart/linux...

[cascardo/linux.git] / Documentation / vm / soft-dirty.txt

diff --git a/Documentation/vm/soft-dirty.txt b/Documentation/vm/soft-dirty.txt
index 9a12a59..55684d1 100644 (file)
--- a/Documentation/vm/soft-dirty.txt
+++ b/Documentation/vm/soft-dirty.txt
@@ -28,6 +28,13 @@ This is so, since the pages are still mapped to physical memory, and thus all
 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