1 ===============
2 Soft-Dirty PTEs
3 ===============
4
5 The soft-dirty is a bit on a PTE which helps t
6 writes to. In order to do this tracking one sh
7
8 1. Clear soft-dirty bits from the task's PTE
9
10 This is done by writing "4" into the ``/p
11 task in question.
12
13 2. Wait some time.
14
15 3. Read soft-dirty bits from the PTEs.
16
17 This is done by reading from the ``/proc/
18 64-bit qword is the soft-dirty one. If se
19 written to since step 1.
20
21
22 Internally, to do this tracking, the writable
23 when the soft-dirty bit is cleared. So, after
24 modify a page at some virtual address the #PF
25 the soft-dirty bit on the respective PTE.
26
27 Note, that although all the task's address spa
28 soft-dirty bits clear, the #PF-s that occur af
29 This is so, since the pages are still mapped t
30 the kernel does is finds this fact out and put
31 bits on the PTE.
32
33 While in most cases tracking memory changes by
34 there is still a scenario when we can lose sof
35 unmaps a previously mapped memory region and t
36 the same place. When unmap is called, the kern
37 including soft dirty bits. To notify user spac
38 memory region renewal the kernel always marks
39 expanded regions) as soft dirty.
40
41 This feature is actively used by the checkpoin
42 can find more details about it on http://criu.
43
44
45 -- Pavel Emelyanov, Apr 9, 2013
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.