linux-kernel - Re: [PATCH 1/6] kmod: add dynamic max concurrent thread count

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Message-ID: <CAB=NE6V-2hhTmOj4bxQBYSwGknZkauPvvJ0vbN4AQ-OMhkPfTA@mail.gmail.com>
Date:   Thu, 25 May 2017 12:01:37 -0700
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Tom Gundersen <teg@...m.no>, Filipe Manana <fdmanana@...e.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        rgoldwyn@...e.com, hare <hare@...e.com>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kselftest@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Aaron Tomlin <atomlin@...hat.com>, rwright@....com,
        Heinrich Schuchardt <xypron.glpk@....de>,
        Michal Marek <mmarek@...e.com>, martin.wilck@...e.com,
        Rusty Russell <rusty@...tcorp.com.au>,
        Jeff Mahoney <jeffm@...e.com>, Ingo Molnar <mingo@...hat.com>,
        Petr Mladek <pmladek@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, shuah@...nel.org,
        DSterba@...e.com, Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>, NeilBrown <neilb@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Jessica Yu <jeyu@...hat.com>,
        Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
Subject: Re: [PATCH 1/6] kmod: add dynamic max concurrent thread count

On Thu, May 25, 2017 at 11:26 AM, Dmitry Torokhov
<dmitry.torokhov@...il.com> wrote:
> On Thu, May 25, 2017 at 08:06:03PM +0200, Luis R. Rodriguez wrote:
>> On Thu, May 25, 2017 at 10:38:40AM -0700, Luis R. Rodriguez wrote:
>> > On Thu, May 25, 2017 at 10:30 AM, Dmitry Torokhov
>> > > There is
>> > > no slippery slope for systems to move away, no need to backport
>> > > anything. We seem to agree that a better solution is possible (throttle
>> > > number of concurrently running modprobes without killing requesters),
>> > > and with that solution the band-aid will no longer be needed.
>> > >
>> > > So please implement and post the proper fix for the issue.
>> >
>> > Alright, will do away with this patch and just go for the jugular of the issue.
>>
>> I gave this some more thought, even if we go with the throttling right away in
>> practice you'll end up with a dmesg notice of a throttle kicking in once you *do*
>
> So remove it. The warning was meaningful when we rejected requests, now
> it is not.

Great.

>> reach this. We are forcing only 50 concurrent threads and making this a static
>> limit with no good reason than 2.3.38 days evaluation from 16 years ago (2000).
>> If we throttle we are going to throttle with a 2.3.38 days limit. And you
>> advocate that ?
>
> Yes. Can you give me reason why slamming the system with more than 50
> modprobes is a good idea in 4.12 days? Does the increased limit
> decreases boot time? By how much?

If in practice we are not hitting the limit the point is moot, and
when we do I agree we can re-evaluate. With my stress test driver on a
test case we can push as hard as bringing out the OOM killer even if
we throttle, fun.

  Luis