On Fri, Apr 22, 2016 at 12:26:52PM +0200, Christoffer Dall wrote: > On Fri, Apr 22, 2016 at 11:17:47AM +0100, Peter Maydell wrote: > > On 22 April 2016 at 11:15, Christoffer Dall <christoffer.d...@linaro.org> > > wrote: > > > Peter just pointed me to a change I remember doing for ARM, so perhaps > > > this fix is the right one? > > > > > > > > > diff --git a/util/oslib-posix.c b/util/oslib-posix.c > > > index d25f671..a36e734 100644 > > > --- a/util/oslib-posix.c > > > +++ b/util/oslib-posix.c > > > @@ -35,7 +35,7 @@ > > > extern int daemon(int, int); > > > #endif > > > > > > -#if defined(__linux__) && (defined(__x86_64__) || defined(__arm__)) > > > +#if defined(__linux__) && (defined(__x86_64__) || defined(__arm__)) || > > > defined(__aarch64__) > > > /* Use 2 MiB alignment so transparent hugepages can be used by KVM. > > > Valgrind does not support alignments larger than 1 MiB, > > > therefore we need special code which handles running on Valgrind. > > > */ > > > > I hadn't realised AArch64 didn't define __arm__. Your extra clause > > wants to be inside the parens for the ||, not outside. > > > > So was the problem just that we weren't passing 2MB as the align > > parameter to qemu_ram_mmap(), and if we do pass 2MB then it does the > > right thing ? > > > Yes, that was essentially the problem. I'll send a proper patch. > > However, Marc pointed out, that we should probably think about improving > on this in the future, because if you're running on a 64K page system > and want huge pages, you have to align at a higher boundary, but I'm on > the other hand not sure such a boundary is always practical on a 64K > system. Which would suggest that we either need to: > > 1) Probe the kernel for the page size and always align to something that > allows huge pages, or > > 2) Let the user specify an option that says it wants to be able to use > THP and only then align to the huge page boundary. > > Not sure...
Probably (1), otherwise the T in THP becomes t, i.e. the use of THP gets slightly less transparent. Though I agree that using THP on 64k page systems isn't always a good choice, I think, in those cases, that users would likely just disable THP for the whole system. drew
