Messages in this thread | | | Date | Mon, 26 Jul 2004 13:18:07 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] Limit number of concurrent hotplug processes |
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Hannes Reinecke <hare@suse.de> wrote: > > > > >> Any comments/suggestions welcome; otherwise please apply. > > > > > > I suggest you just use a semaphore, initialised to a suitable value: > > > > > > static struct semaphore foo = __SEMAPHORE_INITIALIZER(foo, 50); > > > > > > { > > ... > > down(&foo); > > ... > > up(&foo); > > ... > > } > > > Hmm; looks good, but: It's not possible to reliably change the maximum > number of processes on the fly. > > The trivial way of course it when the waitqueue is empty and no > processes are holding the semaphore. But it's quite non-obvious how this > should work if processes are already holding the semaphore. > We would need to wait for those processes to finish, setting the length > of the queue to 0 (to disallow any other process from grabbing the > semaphore), and atomically set the queue length to the new value. > Apart from the fact that we would need a worker thread for that > (otherwise the calling process might block indefinitely), there is no > guarantee that the queue ever will become empty, as hotplug processes > might be generated at any time. > > Or is there an easier way?
Well if you want to increase the maximum number by ten you do:
for (i = 0; i < 10; i++) up(&foo);
and similarly for decreasing the limit. That will involve doing down()s, which will automatically wait for the current number of threads to fall to the desired level.
But I don't really see a need to tune this on the fly - probably the worse problem occurs during bootup when the operator cannot perform tuning.
So a __setup parameter seems to be the best way of providing tunability. Initialise the semaphore in usermodehelper_init(). - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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