[ovs-dev] [PATCH 3/3] util: munlockall() and retry when locked memory allocation fails

Ilya Maximets i.maximets at ovn.org
Fri Mar 26 18:52:18 UTC 2021

On 3/26/21 7:30 PM, Ben Pfaff wrote:
> From: James Page <james.page at ubuntu.com>
> Normally when OVS runs on a server the effective system limit for
> locked memory is unlimited as the ovs-vswitchd runs as the root
> user in the root namespace of the server.
> When OVS is run in a non-priviledged container a system limit will
> apply and its possible that this limit will be reached during
> normal operation.
> If this occurs unlock all memory and re-attempt (re)allocation of
> memory rather than fail and abort.
> If this subsequent attempt also fails abort the process as before.
> Signed-off-by: James Page <james.page at ubuntu.com>
> [blp at ovn.org adapted to cover more cases]
> Signed-off-by: Ben Pfaff <blp at ovn.org>
> ---

Hi, Ben and James.

I'll repeat here what I said in a comment on github.

DPDK uses memory locking for mempool pages and it relies on these
pages not being moved or unloaded, because it uses physical addresses
to configure hardware NICs.  Also, some DPDK drivers are using memory
locking to lock in memory pages that are used for driver-specific
device I/O.  Unlocking any of these pages in runtime will likely crash
the system by NMI if such a page will be moved or swapped without
notifying the device and driver.

Blindly unlocking all the memory is very dangerous.

I'd say it's much more safe to just run OVS without passing --mlockall.
Or we need to itroduce a special cmdline flag to allow dynamic unlocking
and also forbid DPDK initialization if this flag enabled.
And all this should be sufficiently documented.

Best regards, Ilya Maximets.

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