> -----Original Message----- > From: Dave Hansen [mailto:dave.hansen@xxxxxxxxx] > Sent: Tuesday, July 23, 2013 12:01 PM > 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 07/23/2013 08:54 AM, KY Srinivasan wrote: > >> > Adding memory usually requires allocating some large, contiguous areas > >> > of memory for use as mem_map[] and other VM structures. That's really > >> > hard to do under heavy memory pressure. How are you accomplishing this? > > I cannot avoid failures because of lack of memory. In this case I notify the host > of > > the failure and also tag the failure as transient. Host retries the operation after > some > > delay. There is no guarantee it will succeed though. > > You didn't really answer the question. > > You have allocated some large, physically contiguous areas of memory > under heavy pressure. But you also contend that there is too much > memory pressure to run a small userspace helper. Under heavy memory > pressure, I'd expect large, kernel allocations to fail much more often > than running a small userspace helper. I am only reporting what I am seeing. Broadly, I have two main failure conditions to deal with: (a) resource related failure (add_memory() returning -ENOMEM) and (b) not being able to online a segment that has been successfully hot-added. I have seen both these failures under high memory pressure. By supporting "in context" onlining, we can eliminate one failure case. Our inability to online is not a recoverable failure from the host's point of view - the memory is committed to the guest (since hot add succeeded) but is not usable since it is not onlined. > > It _sounds_ like you really want to be able to have the host retry the > operation if it fails, and you return success/failure from inside the > kernel. It's hard for you to tell if running the userspace helper > failed, so your solution is to move what what previously done in > userspace in to the kernel so that you can more easily tell if it failed > or succeeded. > > Is that right? No; I am able to get the proper error code for recoverable failures (hot add failures because of lack of memory). By doing what I am proposing here, we can avoid one class of failures completely and I think this is what resulted in a better "hot add" experience in the guest. K. Y > > _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
