linux-kernel - Re: [PATCH v4 4/4] kmod: throttle kmod thread limit

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Message-ID: <20170628221113.GJ21846@wotan.suse.de>
Date:   Thu, 29 Jun 2017 00:11:13 +0200
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     "Luis R. Rodriguez" <mcgrof@...nel.org>, akpm@...ux-foundation.org,
        jeyu@...hat.com, shuah@...nel.org, rusty@...tcorp.com.au,
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Subject: Re: [PATCH v4 4/4] kmod: throttle kmod thread limit

On Mon, Jun 26, 2017 at 01:38:31PM +0200, Petr Mladek wrote:
> On Fri 2017-06-23 12:20:11, Luis R. Rodriguez wrote:
> > 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    0m16.523s
> > user    0m0.879s
> > sys     0m8.977s
> > 
> > time ./kmod.sh -t 0009
> > real    0m56.080s
> > user    0m0.717s
> > sys     0m10.324s
> > 
> > Signed-off-by: Luis R. Rodriguez <mcgrof@...nel.org>
> 
> All the changes look fine to me. They make perfect sense.

Thanks, I'll peg a

Reviewed-by: Petr Mladek <pmladek@...e.com>

  Luis