Messages in this thread | | | Date | Tue, 15 Jan 2013 14:50:45 -0800 | From | Dave Hansen <> | Subject | Re: [RFCv3][PATCH 1/3] create slow_virt_to_phys() |
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On 01/15/2013 11:46 AM, H. Peter Anvin wrote: > I object to this switch statement. If we are going to create new > primitives, let's create a primitive that embody this and put it in > pgtypes_types.h, especially since it is simply an algorithmic operation:
Yeah, that's a good point. I did at least copy part of the switch from elsewhere in the file, so there's certainly room for consolidating some things.
> static inline unsigned long page_level_size(int level) > { > return (PAGE_SIZE/PGDIR_SIZE) << (PGDIR_SHIFT*level); > } > static inline unsigned long page_level_shift(int level) > { > return (PAGE_SHIFT-PGDIR_SHIFT) + (PGDIR_SHIFT*level); > }
(PAGE_SHIFT-PGDIR_SHIFT) == -27, so this can't possibly work, right?
How about something like this?
/* * Note: this only holds true for pagetable levels where PTEs can be * present. It would break if you used it on the PGD level where PAE * is in use. It basically assumes that the shift between _all_ * adjacent levels of the pagetables are the same as the lowest-level * shift. */ #define PG_SHIFT_PER_LEVEL (PMD_SHIFT-PAGE_SHIFT)
static inline unsigned long page_level_shift(int level) { return PAGE_SHIFT + (level - PG_LEVEL_4K) * PG_SHIFT_PER_LEVEL; } static inline unsigned long page_level_size(int level) { return 1 << page_level_shift(level); }
The generated code for page_level_size() looks pretty good, despite it depending on page_level_shift(), so we might as well leave it defined this way for simplicity:
0000000000400610 <plsize>: 400610: 8d 7c bf fb lea -0x5(%rdi,%rdi,4),%edi 400614: b8 01 00 00 00 mov $0x1,%eax 400619: 8d 4c 3f 0c lea 0xc(%rdi,%rdi,1),%ecx 40061d: d3 e0 shl %cl,%eax 40061f: c3 retq
I'll send out another series doing this.
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