linux-kernel - RE: [PATCH 1/1] Drivers: base: memory: Export symbols for onlining memory blocks

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Message-ID: <4f440c8d96f34711a3f06fb18702a297@SN2PR03MB061.namprd03.prod.outlook.com>
Date:	Thu, 25 Jul 2013 11:14:18 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Michal Hocko <mhocko@...e.cz>, Dave Hansen <dave.hansen@...el.com>
CC:	Dave Hansen <dave@...1.net>,
	"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>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"yinghan@...gle.com" <yinghan@...gle.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"kay@...y.org" <kay@...y.org>
Subject: RE: [PATCH 1/1] Drivers: base: memory: Export symbols for onlining
 memory blocks



> -----Original Message-----
> From: Michal Hocko [mailto:mhocko@...e.cz]
> Sent: Thursday, July 25, 2013 3:57 AM
> To: Dave Hansen
> Cc: KY Srinivasan; Dave Hansen; 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; hannes@...xchg.org;
> yinghan@...gle.com; jasowang@...hat.com; kay@...y.org
> Subject: Re: [PATCH 1/1] Drivers: base: memory: Export symbols for onlining
> memory blocks
> 
> On Wed 24-07-13 14:02:32, Dave Hansen wrote:
> > On 07/24/2013 12:45 PM, KY Srinivasan wrote:
> > > All I am saying is that I see two classes of failures: (a) Our
> > > inability to allocate memory to manage the memory that is being hot added
> > > and (b) Our inability to bring the hot added memory online within a
> reasonable
> > > amount of time. I am not sure the cause for (b) and I was just speculating that
> > > this could be memory related. What is interesting is that I have seen failure
> related
> > > to our inability to online the memory after having succeeded in hot adding the
> > > memory.
> >
> > I think we should hold off on this patch and other like it until we've
> > been sufficiently able to explain how (b) happens.
> 
> Agreed.

As promised, I have sent out the patches for (a) an implementation of an in-kernel API
for onlining  and a consumer for this API. While I don't know the exact reason why the
user mode code is delayed (under some low memory conditions), what is the harm in having
a mechanism to online memory that has been hot added without involving user space code.
Based on Michal's feedback, the onlininig API hides all of the internal details and presents a
generic interface.

Regards,

K. Y



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