On Mon 18-03-13 13:44:05, KY Srinivasan wrote: > > > > -----Original Message----- > > From: Michal Hocko [mailto:mho...@suse.cz] > > Sent: Monday, March 18, 2013 6:53 AM > > To: KY Srinivasan > > Cc: gre...@linuxfoundation.org; linux-kernel@vger.kernel.org; > > de...@linuxdriverproject.org; o...@aepfle.de; a...@canonical.com; > > a...@firstfloor.org; a...@linux-foundation.org; linux...@kvack.org; > > kamezawa.hiroy...@gmail.com; han...@cmpxchg.org; ying...@google.com > > 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
