On Wed, 2015-02-18 at 21:44 +0100, Ingo Molnar wrote: > * Toshi Kani <toshi.kani@xxxxxx> wrote: > > > This patch implements huge I/O mapping capability interfaces on x86. > > > +#ifdef CONFIG_HUGE_IOMAP > > +#ifdef CONFIG_X86_64 > > +#define IOREMAP_MAX_ORDER (PUD_SHIFT) > > +#else > > +#define IOREMAP_MAX_ORDER (PMD_SHIFT) > > +#endif > > +#endif /* CONFIG_HUGE_IOMAP */ > > > +#ifdef CONFIG_HUGE_IOMAP > > Hm, so why is there a Kconfig option for this? It just > complicates things. > > For example the kernel already defaults to mapping itself > with as large mappings as possible, without a Kconfig entry > for it. There's no reason to make this configurable - and > quite a bit of complexity in the patches comes from this > configurability. This Kconfig option was added to disable this feature in case there is an issue. That said, since the patchset also added a new nohugeiomap boot option for the same purpose, I agree that this Kconfig option can be removed. So, I will remove it in the next version. An example of such case is with multiple MTRRs described in patch 0/7. However, I believe it is very unlikely to have such platform/use-case, and it can also be avoided by a driver creating a separate mapping for each MTRR range. Thanks, -Toshi -- 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>