Changes

In order to find out which memory pages have changed, we [http://lwn.net/Articles/546966/ patched] the kernel. Tracking the memory changes consists of two steps:

In order to find out which memory pages have changed, we [http://lwn.net/Articles/546966/ patched] the kernel. Tracking the memory changes consists of two steps:

* Tell the kernel that we want it to keep track of memory changes by particular task by writing 4 into <code>/proc/$pid/clear_refs</code> file.

* ask the kernel to keep track of memory changes (by writing 4 into <code>/proc/$pid/clear_refs</code> file for each $pid we are interested in).

and after a while

and, after a while,

* Get what pages were modified by task by reading its <code>/proc/$pid/pagemap</code> file and looking at so called ''soft-dirty'' bit in the pagemap entries.

* get the list of modified pages of a process by reading its <code>/proc/$pid/pagemap</code> file and looking at so called ''soft-dirty'' bit in the pagemap entries.

On the first step kernel will re-map all the tasks' mapping in read-only manner. If a task will try to write into one of its pages later, a page fault would occur and the kernel would note which page was written to. Reading the <code>pagemap</code> file reveals this information.

During the first step, kernel will re-map all the tasks' mapping in read-only manner. If a task then tries to write into any of its pages, a page fault will occur, and the kernel will note which page is being written to. Reading the <code>pagemap</code> file reveals this information.

== How to use this with CRIU ==

== How to use this with CRIU ==