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? > This is also something that should be coordinated with the -mem-path > refactoring. Oh. There is always refactoring :( -- Alexey
