linux-kernel - Re: 4.4-final: 28 bioset threads on small notebook

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Message-ID: <20160220200432.GB22120@amd>
Date:	Sat, 20 Feb 2016 21:04:32 +0100
From:	Pavel Machek <pavel@....cz>
To:	Mike Snitzer <snitzer@...hat.com>
Cc:	kernel list <linux-kernel@...r.kernel.org>, axboe@...com,
	hch@....de, kent.overstreet@...il.com, neilb@...e.de,
	martin.petersen@...cle.com, dpark@...teo.net,
	ming.l@....samsung.com, dm-devel@...hat.com,
	ming.lei@...onical.com, agk@...hat.com, jkosina@...e.cz,
	geoff@...radead.org, jim@...n.com, pjk1939@...ux.vnet.ibm.com,
	minchan@...nel.org, ngupta@...are.org, oleg.drokin@...el.com,
	andreas.dilger@...el.com
Subject: Re: 4.4-final: 28 bioset threads on small notebook

Hi!

> > > > > I know it is normal to spawn 8 threads for every single function,
> > > > ...
> > > > > but 28 threads?
> > > > > 
> > > > > root       974  0.0  0.0      0     0 ?        S<   Dec08   0:00 [bioset]
> > > > ...
> > > > 
> > > > How many physical block devices do you have?
> > > > 
> > > > DM is doing its part to not contribute to this:
> > > > dbba42d8a ("dm: eliminate unused "bioset" process for each bio-based DM device")
> > > > 
> > > > (but yeah, all these extra 'bioset' threads aren't ideal)
> > > 
> > > Still there in 4.4-final.
> > 
> > ...and still there in 4.5-rc4 :-(.
> 
> You're directing this concern to the wrong person.
> 
> I already told you DM is _not_ contributing any extra "bioset" threads
> (ever since commit dbba42d8a).

Well, sorry about that. Note that l-k is on the cc list, so hopefully
the right person sees it too.

Ok, let me check... it seems that 
54efd50bfd873e2dbf784e0b21a8027ba4299a3e is responsible, thus Kent
Overstreet <kent.overstreet@...il.com> is to blame.

Um, and you acked the patch, so you are partly responsible.

> But in general, these "bioset" threads are a side-effect of the
> late-bio-splitting support.  So is your position on it: "I don't like
> that feature if it comes at the expense of adding resources I can _see_
> for something I (naively?) view as useless"?

> Just seems... naive... but you could be trying to say something else
> entirely.

> Anyway, if you don't like something: understand why it is there and then
> try to fix it to your liking (without compromising why it was there to
> begin with).

Well, 28 kernel threads on a notebook is a bug, plain and simple. Do
you argue it is not?

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html