[CRIU] [PATCH 00/12] Introduce custom per-task service fds placement

[Andrei Vagin]

On Tue, Dec 26, 2017 at 06:45:46PM +0300, Kirill Tkhai wrote:
> Currently, service fds are bounded to rlimit(RLIMIT_NOFILE).
> This brings problems with memory usage, because service fds
> forces kernel to allocate big files_struct for every task,
> and the container consumes much more memory, than it used
> before dump. In some situations this even may lead to restore
> fail because of enough memory absence in cgroup or on node.
> 
> This patchset reworks service fds placement, and places
> the service fds in custom place for every task in dependence
> of task's biggest fd used on dump. This reduces kernel-allocated
> files_struct in significant way, and make container use less
> memory.
> 
> The patchset consists of two parts. Patches [1-4/12] reworks
> ctl tty crutch we used before, and makes ctl tty to restore
> in generic file engine way. This change is good enough by its
> own, and it has to be made separately earlier, but now is
> the time to stop delaying, and to remove all the crutch, because
> this is need for the second part.
> 
> The second part of patchset places service fds in dependence
> of task's used fds as described in start of topic. See patches
> [5-12/12] for details of that.
> 
> Patch [12/12] actually makes service fds "per-task placed".
> 
> https://travis-ci.org/tkhai/criu/builds/321817890

I have another idea. Currently we have all problems with descriptors,
because we want to restore them too early. We can do a trick like we do
for mappings. We can restore descriptors and don't care about their
numbers, and then after retoring evething, we can move them to
required numbers.

This trick has to simplify a lot of place. For example, we will not need
find_unused_fd().

> ---
> 
> Kirill Tkhai (12):
>       files: Close ctl tty via generic engine
>       files: Move prepare_ctl_tty() to criu/tty.c
>       files: Move CTL_TTY_OFF fixup to generic file engine
>       files: Kill unused CTL_TTY_OFF leftovers
>       files: Rename service_fd_rlim_cur to service_fd_base_cur
>       files: Count inh_fd_max
>       files: Pass pstree_item argument to clone_service_fd()
>       files: Close old service fd in clone_service_fd()
>       files: Do setup_newborn_fds() later
>       files: Refactor clone_service_fd()
>       files: Prepare clone_service_fd() for overlaping ranges.
>       files: Make tasks set their own service_fd_base
> 
> 
>  criu/cr-restore.c        |   14 +++--
>  criu/files.c             |   45 +++-------------
>  criu/include/files.h     |    3 +
>  criu/include/servicefd.h |    4 -
>  criu/include/tty.h       |    2 -
>  criu/include/util.h      |    2 +
>  criu/tty.c               |  127 +++++++++++++++++++++++++++++++++++++++++++---
>  criu/util.c              |  101 ++++++++++++++++++++++++++-----------
>  images/fdinfo.proto      |    1 
>  9 files changed, 214 insertions(+), 85 deletions(-)
> 
> --
> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>