Messages in this thread | | | Subject | Re: [PATCHv3 03/11] arm64: Introduce helpers for page table levels | From | "Suzuki K. Poulose" <> | Date | Thu, 15 Oct 2015 14:48:47 +0100 |
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On 15/10/15 14:30, Christoffer Dall wrote: > On Thu, Oct 15, 2015 at 02:14:22PM +0100, Suzuki K. Poulose wrote: >> On 15/10/15 13:44, Mark Rutland wrote: >>> On Thu, Oct 15, 2015 at 01:37:35PM +0200, Christoffer Dall wrote: >>>> On Wed, Oct 14, 2015 at 12:20:26PM +0100, Suzuki K. Poulose wrote:
>> * The maximum number of levels supported by the architecture is 4. Hence at starting >> * at level n, we hanve (4 - n) levels of translation. So, the total number of bits > > nit: s/hanve/have/
Fixed.
> >> * mapped by an entry at level n is : >> * >> * ((4 - n) - 1) * (PAGE_SHIFT - 3) + PAGE_SHIFT >> * >> * Rearranging it a bit we get : >> * (4 - n) * (PAGE_SHIFT - 3) + 3 >> */ >> >> Or we could use the formula without rearranging. >> > Either way, even I get it now. > > Thanks for the explanation!!
:). I was involved too much in these calculations that, the formula looked obvious to me, when I wrote it. But yes, I did realise that it is indeed complicated, once I really started looking at explaining why I wrote it so. Thanks for being patient :) and complaining peacefully !
Btw, I have a revised (hopefully better) version here :
/* * Size mapped by an entry at level n ( 0 <= n <= 3) * We map (PAGE_SHIFT - 3) at all translation levels and PAGE_SHIFT bits * in the final page. The maximum number of translation levels supported by * the architecture is 4. Hence, starting at at level n, we have further * ((4 - n) - 1) levels of translation excluding the offset within the page. * So, the total number of bits mapped by an entry at level n is : * * ((4 - n) - 1) * (PAGE_SHIFT - 3) + PAGE_SHIFT * * Rearranging it a bit we get : * (4 - n) * (PAGE_SHIFT - 3) + 3 */
> > Assuming some version of this goes in: > > Acked-by: Christoffer Dall <christoffer.dall@linaro.org> >
Thanks. I lost two interview questions though ;)
Suzuki
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