David Miller wrote: [Wed Nov 13 2013, 02:18:41AM EST] > > The impetus for this is that we would like to move to 64-bit PMDs and > PGDs, but that would result in only supporting a 42-bit address space > with the current page table layout. It'd be nice to support at least > 43-bits. > > The reason we'd end up with only 42-bits after making PMDs and PGDs > 64-bit is that we only use half-page sized PTE tables in order to make > PMDs line up to 4MB, the hardware huge page size we use. > > So what we do here is we make huge pages 8MB, and fabricate them using > 4MB hw TLB entries. > > Facilitate this by providing a "REAL_HPAGE_SHIFT" which is used in > places that really need to operate on hardware 4MB pages. > > Use full pages (512 entries) for PTE tables, and adjust PMD_SHIFT, > PGD_SHIFT, and the build time CPP test as needed. Use a CPP test to > make sure REAL_HPAGE_SHIFT and the _PAGE_SZHUGE_* we use match up. > > This makes the pgtable cache completely unused, so remove the code > managing it and the state used in mm_context_t. Now we have less > spinlocks taken in the page table allocation path. > > The technique we use to fabricate the 8MB pages is to transfer bit 22 > from the missing virtual address into the PTEs physical address field. > That takes care of the transparent huge pages case. > > For hugetlb, we fill things in at the PTE level and that code already > puts the sub huge page physical bits into the PTEs, based upon the > offset, so there is nothing special we need to do. It all just works > out. > > So, a small amount of complexity in the THP case, but this code is > about to get much simpler when we move the 64-bit PMDs as we can move > away from the fancy 32-bit huge PMD encoding and just put a real PTE > value in there. > > With bug fixes and help from Bob Picco. > > Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> > --- Acked-by: Bob Picco <bob.picco@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
