kmod: throttle kmod thread limit
If we reach the limit of modprobe_limit threads running the next
request_module() call will fail. The original reason for adding
a kill was to do away with possible issues with in old circumstances
which would create a recursive series of request_module() calls.
We can do better than just be super aggressive and reject calls
once we've reached the limit by simply making pending callers wait
until the threshold has been reduced, and then throttling them in,
one by one.
This throttling enables requests over the kmod concurrent limit to
be processed once a pending request completes. Only the first item
queued up to wait is woken up. The assumption here is once a task
is woken it will have no other option to also kick the queue to check
if there are more pending tasks -- regardless of whether or not it
was successful.
By throttling and processing only max kmod concurrent tasks we ensure
we avoid unexpected fatal request_module() calls, and we keep memory
consumption on module loading to a minimum.
With x86_64 qemu, with 4 cores, 4 GiB of RAM it takes the following run
time to run both tests:
time ./kmod.sh -t 0008
real 0m16.366s
user 0m0.883s
sys 0m8.916s
time ./kmod.sh -t 0009
real 0m50.803s
user 0m0.791s
sys 0m9.852s
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
2 files changed
