On 21.02.2014, at 13:56, Alexey Kardashevskiy <a...@ozlabs.ru> wrote:
> On 02/21/2014 07:57 PM, Alexander Graf wrote: >> >> On 21.02.2014, at 05:57, Alexey Kardashevskiy <a...@ozlabs.ru> wrote: >> >>> On 02/10/2014 05:32 PM, Alexey Kardashevskiy wrote: >>>> At the moment if the user asked for huge pages and there is no more huge >>>> pages, QEMU prints warning and falls back to the anonymous memory >>>> allocator which is quite easy not to notice. QEMU also does so even >>>> if the user specified -mem-prealloc and it seems wrong as the user >>>> specifically requested huge pages for the entire RAM but QEMU failed to do >>>> so and continued. On PPC64 this will produce a fragile guest as QEMU >>>> tells the guest via device-tree that it can use huge pages when it >>>> actually cannot. >>>> >>>> This adds message+exit if RAM cannot be preallocated from huge pages. >>> >>> >>> Too bad? Should I increase my personal pinging timeout from 1 to 2 weeks to >>> avoid annoying the community? :) Thanks! >> > >> The patch changes the semantics of -mem-prealloc from "make sure all >> RAM is mapped" to "make sure all RAM is mapped and is backed by huge >> pages if we use huge pages" and thus is just plain wrong. > > ? I did actually expect it to alloc RAM from hugepages only. Otherwise > there is no point in mem-prealloc. Yes, I am ignorant, I know. > >> The real question is why are we allowing sparsely mapped huge page > backing at all? Should we change that? Do we need a new flag for this to > specify "yes, I do want all my pages backed by -mem-path"? > > > ? Add a switch to -mem-path saying "yes I really want -mem-path"? Sorry, I > lost you here. -mem-path + -mem-prealloc - like this is not enough? Why > would I specify -mem-path after all if I did not want RAM to backed by huge > pages? I think it makes sense to disable any fallback for -mem-path, so that it always only allocates RAM pages from the -mem-path pool. But this is a big change from how it used to work before and thus needs to be properly coordinated. Paolo, Peter, any thoughts here? Version 2.0 might be a good fit for such a change ;). Alex
