On Wed, 2014-09-10 at 11:26 -0700, Andy Lutomirski wrote: > On Wed, Sep 10, 2014 at 9:51 AM, Toshi Kani <toshi.kani@xxxxxx> wrote: > > This patch changes reserve_memtype() to handle the WT cache mode. > > When PAT is not enabled, it continues to set UC- to *new_type for > > any non-WB request. > > > > When a target range is RAM, reserve_ram_pages_type() fails for WT > > for now. This function may not reserve a RAM range for WT since > > reserve_ram_pages_type() uses the page flags limited to three memory > > types, WB, WC and UC. > > Should it fail if WT is unavailable due to errata? More generally, > how are all of the do_something_wc / do_something_wt / > do_something_nocache helpers supposed to handle unsupported types? When WT is unavailable due to the PAT errata, it does not fail but gets redirected to UC-. Similarly, when PAT is disabled, WT gets redirected to UC- as well. The failure case above is a run-time error when WT is enabled and is targeted to RAM. In this case, reserve_memtype() fails and sets UC- to *new_type due to the limitation in page tables. set_memory_xzy() interfaces do not retry with new_type, but return an error. I think this makes sense since the caller should receive this error as this case is a bug in the code (while running it on an old system is not a bug). 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>