From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx189.postini.com [74.125.245.189]) by kanga.kvack.org (Postfix) with SMTP id 9ED076B0034 for ; Thu, 25 Jul 2013 11:50:29 -0400 (EDT) Received: from mail137-co1 (localhost [127.0.0.1]) by mail137-co1-R.bigfish.com (Postfix) with ESMTP id 460BEDC0170 for ; Thu, 25 Jul 2013 15:50:27 +0000 (UTC) Received: from CO1EHSMHS022.bigfish.com (unknown [10.243.78.249]) by mail137-co1.bigfish.com (Postfix) with ESMTP id 9579860004C for ; Thu, 25 Jul 2013 15:50:23 +0000 (UTC) Received: from mail214-ch1 (localhost [127.0.0.1]) by mail214-ch1-R.bigfish.com (Postfix) with ESMTP id C1F81140235 for ; Thu, 25 Jul 2013 15:50:00 +0000 (UTC) From: KY Srinivasan Subject: RE: [PATCH 1/1] Drivers: base: memory: Export symbols for onlining memory blocks Date: Thu, 25 Jul 2013 15:49:00 +0000 Message-ID: <828d748273884d6f9c24b658964f97c3@SN2PR03MB061.namprd03.prod.outlook.com> References: <1374261785-1615-1-git-send-email-kys@microsoft.com> <20130722123716.GB24400@dhcp22.suse.cz> <51EEA11D.4030007@intel.com> <3318be0a96cb4d05838d76dc9d088cc0@SN2PR03MB061.namprd03.prod.outlook.com> <51EEA89F.9070309@intel.com> <9f351a549e76483d9148f87535567ea0@SN2PR03MB061.namprd03.prod.outlook.com> <51F00415.8070104@sr71.net> <51F040E8.1030507@intel <51F13E51.7040808@sr71.net> In-Reply-To: <51F13E51.7040808@sr71.net> Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: Michal Hocko , "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" > -----Original Message----- > From: Dave Hansen [mailto:dave@sr71.net] > Sent: Thursday, July 25, 2013 11:04 AM > To: KY Srinivasan > Cc: Michal Hocko; gregkh@linuxfoundation.org; linux-kernel@vger.kernel.or= g; > 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 onlini= ng > memory blocks >=20 > On 07/25/2013 04:14 AM, KY Srinivasan wrote: > > As promised, I have sent out the patches for (a) an implementation of a= n 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 t= he > harm in having > > a mechanism to online memory that has been hot added without involving = user > space code. >=20 > KY, your potential problem, not being able to online more memory because > of a shortage of memory, is a serious one. All I can say is that the online is not happening within the allowed time (= 5 seconds in the current code). >=20 > However, this potential issue exists in long-standing code, and > potentially affects all users of memory hotplug. The problem has not > been described in sufficient detail for the rest of the developers to > tell if you are facing a new problem, or whether *any* proposed solution > will help the problem you face. >=20 > Your propsed solution changes the semantics of existing user/kernel > interfaces, duplicates existing functionality, and adds code complexity > to the kernel. How so? All I am doing is to use the existing infrastructure to online memory. The only change I have made is to export an API that allows onlining without involving any user space code. I don't see how this adds complexity to the kernel. This would be an useful extension as can be seen from its usage in the Hyper-V balloon driver. In my particular use case, I need to wait for the memory to be onlined befo= re I can proceed to hot add the next chunk. This synchronization can be comple= tely avoided if we can avoid the involvement of user level code. I would submit = to you that this is a valid use case that we ought to be able to support. Regards, K. Y -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org