Difference between revisions of "Memory dumping and restoring"
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Currently memory dumping depends on 3 big technologies: | Currently memory dumping depends on 3 big technologies: | ||
| − | * /proc/pid/map_files/ directory with links | + | * /proc/pid/smaps file and /proc/pid/map_files/ directory with links are used to determine |
| − | ** | + | ** memory areas in use by task |
| − | ** shared memory "identifier" to | + | ** file is mapped (if any) |
| − | * proc pagemap file | + | ** shared memory "identifier" to resolve the MAP_SHARED areas |
| − | * Ptrace SEIZE is used to grab pages from task's VM into pipe (with vmsplice) | + | * /proc/pid/pagemap file that reveals important flags |
| + | ** ''present'' indicates that the physical page is there. Non-present pages are not dumped. | ||
| + | ** ''anonymoys'' for the MAP_FILE | MAP_PRIVATE mapping indicate that the page in question is already COW-ed from the file's. Not-anonymous pages are not dumped as they are still in sync with the file | ||
| + | ** ''soft-dirty'' bit is used by [[memory changes tracker]] | ||
| + | * Ptrace SEIZE that is used to grab pages from task's VM into pipe (with vmsplice) | ||
=== Restoring === | === Restoring === | ||
Revision as of 17:22, 28 January 2015
How it works now
Dumping
Currently memory dumping depends on 3 big technologies:
- /proc/pid/smaps file and /proc/pid/map_files/ directory with links are used to determine
- memory areas in use by task
- file is mapped (if any)
- shared memory "identifier" to resolve the MAP_SHARED areas
- /proc/pid/pagemap file that reveals important flags
- present indicates that the physical page is there. Non-present pages are not dumped.
- anonymoys for the MAP_FILE | MAP_PRIVATE mapping indicate that the page in question is already COW-ed from the file's. Not-anonymous pages are not dumped as they are still in sync with the file
- soft-dirty bit is used by memory changes tracker
- Ptrace SEIZE that is used to grab pages from task's VM into pipe (with vmsplice)
Restoring
This one depends only on the /proc/pid/map_files/ to restore the shmem regions -- tasks just open some other's link and map it to create shmem region. The pages restoration just writes page data "in place".
Non linear mappings
Currently we don't support non-linear mappings (fail dump if present)