pre-dump support #808
pre-dump support #808
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adrianreber
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the PR is still in Draft, is there anything more left to do before we can merge? |
There are still a few libcriu changes under review and I would like to wait merging this until it is merged on the CRIU side:
I do not expect the API to change on the CRIU side during review, but still, if it works for you, we should wait for a couple of days. |
sure, that works for me. |
CRIU supports the concept of pre-copy migration. Instead of creating a complete checkpoint of a process it is possible to only write the memory of the process to disk while the process keeps on running. The first memory only checkpoint can then be transferred to the migration destination. During the transfer time it is possible take a second checkpoint which will only write the memory pages to disk that have changed since the previous checkpoint. This way it can be possible that the second checkpoint is much smaller while the process keeps on running which also means that the amount of data which needs to be transferred to the migration destination might be smaller and thus the migration downtime can be reduced. This only makes sense if the number of memory pages which are changing is rather small. There is no limit on the number pre-copy iterations. This commit takes the interface as implemented in runc and implements it for crun. Podman already uses the pre-dump as implemented by runc. This commit also makes sure that the underlying software stack supports the pre-dump mechanism. CRIU uses the kernel's dirty page tracking and it is not available on all architectures (aarch64 does not implement it) or might not be enabled in the kernel. If the user wants to use pre-dump on a system without dirty page tracking crun will fail early and inform the user. This crun pre-dump implementation relies on libcriu interfaces which are not yet part of the latest release (3.16.1). So at least 3.16.2 or 3.17 is required to use pre-dump in combination with crun. Signed-off-by: Adrian Reber <areber@redhat.com>
This documents the two pre-copy migration related checkpoint options --pre-dump and --parent-path.
This adds the memhog command to tests/init. This command requires a parameter telling init how many MB of memory should be allocated. In addition to allocation the memory and writing each page once, the memhog command changes a memory page each 0.1 seconds. This is useful to test crun's pre-dump support. Signed-off-by: Adrian Reber <areber@redhat.com>
This extends the checkpoint/restore test to also test the newly implemented pre-dump support. Signed-off-by: Adrian Reber <areber@redhat.com>
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@adrianreber I am planning to cut a release in the next days (most likely tomorrow). Would it be safer to wait next release to merge these changes? |
Yes. One of the depending PRs has been merged and the other one is really close, but this can wait for the next release. |
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@adrianreber deps are merged. Can we merge this one as well? |
Yes. This will be still disabled in CI because it depends on a new release, but we are already talking about a new release. As soon that is available crun CI should pick it up. |
CRIU supports the concept of pre-copy migration. Instead of creating a
complete checkpoint of a process it is possible to only write the memory
of the process to disk while the process keeps on running. The first
memory only checkpoint can then be transferred to the migration
destination. During the transfer time it is possible take a second
checkpoint which will only write the memory pages to disk that have
changed since the previous checkpoint. This way it can be possible that
the second checkpoint is much smaller while the process keeps on running
which also means that the amount of data which needs to be transferred
to the migration destination might be smaller and thus the migration
downtime can be reduced. This only makes sense if the number of memory
pages which are changing is rather small. There is no limit on the
number pre-copy iterations.
This commit takes the interface as implemented in runc and implements it
for crun. Podman already uses the pre-dump as implemented by runc.
This commit also makes sure that the underlying software stack supports
the pre-dump mechanism. CRIU uses the kernel's dirty page tracking and
it is not available on all architectures (aarch64 does not implement it)
or might not be enabled in the kernel. If the user wants to use pre-dump
on a system without dirty page tracking crun will fail early and inform
the user.
This crun pre-dump implementation relies on libcriu interfaces which are
not yet part of the latest release (3.16.1). So at least 3.16.2 or 3.17
is required to use pre-dump in combination with crun.