From: KY Srinivasan <kys@microsoft.com>
To: Michal Hocko <mhocko@suse.cz>, Dave Hansen <dave.hansen@intel.com>
CC: Dave Hansen <dave@sr71.net>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "devel@linuxdriverproject.org" <devel@linuxdriverproject.org>,
        "olaf@aepfle.de" <olaf@aepfle.de>,
        "apw@canonical.com" <apw@canonical.com>,
        "andi@firstfloor.org" <andi@firstfloor.org>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "kamezawa.hiroyuki@gmail.com" <kamezawa.hiroyuki@gmail.com>,
        "hannes@cmpxchg.org" <hannes@cmpxchg.org>,
        "yinghan@google.com" <yinghan@google.com>,
        "jasowang@redhat.com" <jasowang@redhat.com>,
        "kay@vrfy.org" <kay@vrfy.org>
Subject: RE: [PATCH 1/1] Drivers: base: memory: Export symbols for onlining
 memory blocks
Thread-Topic: [PATCH 1/1] Drivers: base: memory: Export symbols for onlining
 memory blocks
Thread-Index: AQHOhLBUexA6H+ozR02R0nup8ZuRHJlwpwQAgAGspICAABWHgIAABmSQgAACj4CAAA/eQIABjleAgAArP0CAAB1DAIAAtuGAgAAyoQA=
Date: Thu, 25 Jul 2013 11:14:18 +0000
Message-ID: <4f440c8d96f34711a3f06fb18702a297@SN2PR03MB061.namprd03.prod.outlook.com>
References: <1374261785-1615-1-git-send-email-kys@microsoft.com>
 <20130722123716.GB24400@dhcp22.suse.cz>
 <e06fced3ca42408b980f8aa68f4a29f3@SN2PR03MB061.namprd03.prod.outlook.com>
 <51EEA11D.4030007@intel.com>
 <3318be0a96cb4d05838d76dc9d088cc0@SN2PR03MB061.namprd03.prod.outlook.com>
 <51EEA89F.9070309@intel.com>
 <9f351a549e76483d9148f87535567ea0@SN2PR03MB061.namprd03.prod.outlook.com>
 <51F00415.8070104@sr71.net>
 <d1f80c05986b439cbeef12bcd595b264@BLUPR03MB050.namprd03.prod.outlook.com>
 <51F040E8.1030507@intel.com> <20130725075705.GD12818@dhcp22.suse.cz>
In-Reply-To: <20130725075705.GD12818@dhcp22.suse.cz>
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> -----Original Message-----
> From: Michal Hocko [mailto:mhocko@suse.cz]
> Sent: Thursday, July 25, 2013 3:57 AM
> To: Dave Hansen
> Cc: KY Srinivasan; Dave Hansen; gregkh@linuxfoundation.org; linux-
> kernel@vger.kernel.org; devel@linuxdriverproject.org; olaf@aepfle.de;
> apw@canonical.com; andi@firstfloor.org; akpm@linux-foundation.org; linux-
> mm@kvack.org; kamezawa.hiroyuki@gmail.com; hannes@cmpxchg.org;
> yinghan@google.com; jasowang@redhat.com; kay@vrfy.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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