On Mon 18-03-13 13:44:05, KY Srinivasan wrote: > > > > -----Original Message----- > > From: Michal Hocko [mailto:mhocko@xxxxxxx] > > Sent: Monday, March 18, 2013 6:53 AM > > To: KY Srinivasan > > Cc: 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 > > Subject: Re: [PATCH 2/2] Drivers: hv: balloon: Support 2M page allocations for > > ballooning > > > > On Sat 16-03-13 14:42:05, K. Y. Srinivasan wrote: > > > While ballooning memory out of the guest, attempt 2M allocations first. > > > If 2M allocations fail, then go for 4K allocations. In cases where we > > > have performed 2M allocations, split this 2M page so that we can free this > > > page at 4K granularity (when the host returns the memory). > > > > Maybe I am missing something but what is the advantage of 2M allocation > > when you split it up immediately so you are not using it as a huge page? > > The Hyper-V ballooning protocol specifies the pages being ballooned as > page ranges - start_pfn: number_of_pfns. So, when the guest balloon > is inflating and I am able to allocate 2M pages, I will be able to > represent 512 contiguous pages in one 64 bit entry and this makes the > ballooning operation that much more efficient. The reason I split the > page is that the host does not guarantee that when it returns the > memory to the guest, it will return in any particular granularity and > so I have to be able to free this memory in 4K granularity. This is > the corner case that I will have to handle. Thanks for the clarification. I think this information would be valuable in the changelog. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>