linux-kernel - Re: [RFC v2 3/6] kthread: warn on kill signal if not OOM

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Date:	Thu, 11 Sep 2014 12:59:25 -0700
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Tejun Heo <tj@...nel.org>,
	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	Lennart Poettering <lennart@...ttering.net>,
	Kay Sievers <kay@...y.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Wu Zhangjin <falcon@...zu.com>, Takashi Iwai <tiwai@...e.de>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>, hare@...e.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Joseph Salisbury <joseph.salisbury@...onical.com>,
	Benjamin Poirier <bpoirier@...e.de>,
	Santosh Rastapur <santosh@...lsio.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Tim Gardner <tim.gardner@...onical.com>,
	Pierre Fersing <pierre-fersing@...rref.org>,
	Nagalakshmi Nandigama <nagalakshmi.nandigama@...gotech.com>,
	Praveen Krishnamoorthy <praveen.krishnamoorthy@...gotech.com>,
	Sreekanth Reddy <sreekanth.reddy@...gotech.com>,
	Abhijit Mahajan <abhijit.mahajan@...gotech.com>,
	Cas ey Leedom <leedom@...lsio.com>,
	Hariprasad S <hariprasad@...lsio.com>,
	MPT-FusionLinux.pdl@...gotech.com,
	Linux SCSI List <linux-scsi@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [RFC v2 3/6] kthread: warn on kill signal if not OOM


On Tue, 2014-09-09 at 16:01 -0700, Dmitry Torokhov wrote:
> On Tuesday, September 09, 2014 03:46:23 PM James Bottomley wrote:
> > On Wed, 2014-09-10 at 07:41 +0900, Tejun Heo wrote:
> > > 
> > > The thing is that we have to have dynamic mechanism to listen for
> > > device attachments no matter what and such mechanism has been in place
> > > for a long time at this point.  The synchronous wait simply doesn't
> > > serve any purpose anymore and kinda gets in the way in that it makes
> > > it a possibly extremely slow process to tell whether loading of a
> > > module succeeded or not because the wait for the initial round of
> > > probe is piggybacked.
> > 
> > OK, so we just fire and forget in userland ... why bother inventing an
> > elaborate new infrastructure in the kernel to do exactly what
> > 
> > modprobe <mod> &
> > 
> > would do?
> 
> Just so we do not forget: we also want the no-modules case to also be able
> to probe asynchronously so that a slow device does not stall kernel booting.

Yes, but we mostly do this anyway.  SCSI for instance does asynchronous
scanning of attached devices (once the cards are probed) but has a sync
point for ordering.

The problem of speeding up boot is different from the one of init
processes killing modprobes.  There are elements in common, but by and
large the biggest headaches at least in large device number boots have
already been tackled by the enterprise crowd (they don't like their
S390's or 1024 core NUMA systems taking half an hour to come up).

James


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