> -----Original Message----- > From: Dave Hansen [mailto:dave@xxxxxxxx] > Sent: Thursday, July 25, 2013 11:04 AM > To: KY Srinivasan > Cc: Michal Hocko; gregkh@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx; apw@xxxxxxxxxxxxx; > andi@xxxxxxxxxxxxxx; akpm@xxxxxxxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; > kamezawa.hiroyuki@xxxxxxxxx; hannes@xxxxxxxxxxx; yinghan@xxxxxxxxxx; > jasowang@xxxxxxxxxx; kay@xxxxxxxx > Subject: Re: [PATCH 1/1] Drivers: base: memory: Export symbols for onlining > memory blocks > > On 07/25/2013 04:14 AM, KY Srinivasan wrote: > > 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. > > 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). > > 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. > > 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 before I can proceed to hot add the next chunk. This synchronization can be completely 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 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
