mirror of
https://github.com/torvalds/linux.git
synced 2024-09-21 15:33:19 +00:00
040fa02077
This is the implementation of the soft-dirty bit concept that should help keep track of changes in user memory, which in turn is very-very required by the checkpoint-restore project (http://criu.org). To create a dump of an application(s) we save all the information about it to files, and the biggest part of such dump is the contents of tasks' memory. However, there are usage scenarios where it's not required to get _all_ the task memory while creating a dump. For example, when doing periodical dumps, it's only required to take full memory dump only at the first step and then take incremental changes of memory. Another example is live migration. We copy all the memory to the destination node without stopping all tasks, then stop them, check for what pages has changed, dump it and the rest of the state, then copy it to the destination node. This decreases freeze time significantly. That said, some help from kernel to watch how processes modify the contents of their memory is required. The proposal is to track changes with the help of new soft-dirty bit this way: 1. First do "echo 4 > /proc/$pid/clear_refs". At that point kernel clears the soft dirty _and_ the writable bits from all ptes of process $pid. From now on every write to any page will result in #pf and the subsequent call to pte_mkdirty/pmd_mkdirty, which in turn will set the soft dirty flag. 2. Then read the /proc/$pid/pagemap2 and check the soft-dirty bit reported there (the 55'th one). If set, the respective pte was written to since last call to clear refs. The soft-dirty bit is the _PAGE_BIT_HIDDEN one. Although it's used by kmemcheck, the latter one marks kernel pages with it, while the former bit is put on user pages so they do not conflict to each other. This patch: A new clear-refs type will be added in the next patch, so prepare code for that. [akpm@linux-foundation.org: don't assume that sizeof(enum clear_refs_types) == sizeof(int)] Signed-off-by: Pavel Emelyanov <xemul@parallels.com> Cc: Matt Mackall <mpm@selenic.com> Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> Cc: Glauber Costa <glommer@parallels.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
||
|---|---|---|
| .. | ||
| array.c | ||
| base.c | ||
| cmdline.c | ||
| consoles.c | ||
| cpuinfo.c | ||
| devices.c | ||
| fd.c | ||
| fd.h | ||
| generic.c | ||
| inode.c | ||
| internal.h | ||
| interrupts.c | ||
| Kconfig | ||
| kcore.c | ||
| kmsg.c | ||
| loadavg.c | ||
| Makefile | ||
| meminfo.c | ||
| namespaces.c | ||
| nommu.c | ||
| page.c | ||
| proc_devtree.c | ||
| proc_net.c | ||
| proc_sysctl.c | ||
| proc_tty.c | ||
| root.c | ||
| self.c | ||
| softirqs.c | ||
| stat.c | ||
| task_mmu.c | ||
| task_nommu.c | ||
| uptime.c | ||
| version.c | ||
| vmcore.c | ||