[CRIU] CRIU vs DMTCP

[Andrew Vagin]

On Sun, Jan 20, 2013 at 11:14:02PM +0200, Andres Toomsalu wrote:
> Hi,
> 
> Maybe a stupid question - but can anybody comment what are the implementation
> differences or reasoning between CRIU and DMTCP (dmtcp.sourceforge.net)?

CRIU can dump a task without preparations. DMTCP can dump only prepared
tasks.

"""
A DMTCP coordinator process is created on a host (default: localhost).
As new processes are created (via fork or ssh), the LD_PRELOAD
environment variable (supported by the Linux loader) is used to preload
the DMTCP library (dmtcphijack.so). That library runs before the routine
main(). It creates a second thread (DMTCP checkpoint thread). The
checkpoint thread then creates a socket to the DMTCP coordinator and
registers itself. The checkpoint thread also creates a signal handler
(SIGUSR2 by default)
"""

CRIU doesn't affect behavior of applications before and after
checkpoint/restore. CRIU is independent from GLIBC and other libraries.
DMTCP sets wrappers on a few system calls, so it can change behavior of
applications. Probably DMCTP can't dump static linked programs and
programs, which call syscall directly.

"""
The run-time overhead of DMTCP is essentially zero. When there is no
checkpoint or restart in process, DMTCP code will run only within DMTCP
wrappers around certain less frequently used system calls. Examples of
such wrappers are wrappers for open(), getpid(), socketpair(), etc.
"""

DMTCP doesn't support namespaces, so it can not dump Linux Containers.

DMTCP virtualizes PID-s in user-space, actually a task is restored with
another pid. It may be prefered in some cases.

I'm not sure that DMCTP can restore anonymous shared memory correctly.

Probably DMTCP can't restore TCP connections, pending signals, zombies,
signalfd, file locks, epoll, etc.

I found all information about DMCTP here http://dmtcp.sourceforge.net/.
Sorry if I'm mistaken somewhere.

CRIU is the next stage in the evolution of Linux C/R. It will be able to
do all things, which could do all previous projects, so let's
consolidate our forces on this project;)

> 
> Kind regards,
> -- 
> ----------------------------------------------
> Andres Toomsalu, andres at opennodecloud.com
> 

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