linux-kernel - RE: [PATCH 2/2] Drivers: hv: balloon: Online the hot-added memory "in context"

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Date:	Wed, 24 Jul 2013 21:10:03 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Dave Hansen <dave@...1.net>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"kamezawa.hiroyuki@...il.com" <kamezawa.hiroyuki@...il.com>,
	"mhocko@...e.cz" <mhocko@...e.cz>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"yinghan@...gle.com" <yinghan@...gle.com>
Subject: RE: [PATCH 2/2] Drivers: hv: balloon: Online the hot-added memory
 "in context"



> -----Original Message-----
> From: Dave Hansen [mailto:dave@...1.net]
> Sent: Wednesday, July 24, 2013 5:04 PM
> To: KY Srinivasan
> Cc: gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org;
> devel@...uxdriverproject.org; olaf@...fle.de; apw@...onical.com;
> andi@...stfloor.org; akpm@...ux-foundation.org; linux-mm@...ck.org;
> kamezawa.hiroyuki@...il.com; mhocko@...e.cz; hannes@...xchg.org;
> yinghan@...gle.com
> Subject: Re: [PATCH 2/2] Drivers: hv: balloon: Online the hot-added memory "in
> context"
> 
> On 07/24/2013 02:29 PM, K. Y. Srinivasan wrote:
> >  		/*
> > -		 * Wait for the memory block to be onlined.
> > -		 * Since the hot add has succeeded, it is ok to
> > -		 * proceed even if the pages in the hot added region
> > -		 * have not been "onlined" within the allowed time.
> > +		 * Before proceeding to hot add the next segment,
> > +		 * online the segment that has been hot added.
> >  		 */
> > -		wait_for_completion_timeout(&dm_device.ol_waitevent,
> 5*HZ);
> > +		online_memory_block(start_pfn);
> 
> Ahhhhh....  You've got a timeout in the code in order to tell the
> hypervisor that you were successfully able to add the memory?  The
> userspace addition code probably wasn't running within this timeout
> period.  right?

As I have always said, the onlining would not occur within a specified amount
of time (under some conditions). The timeout here is to ensure that we are able 
to online the memory before attempting to hot-add more memory. With the ability
to online memory from within the kernel, we don't need this timeout and the code is
much more predictable.

Regards,

K. Y



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