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Re: [RFC v6 02/62] powerpc: Free up four 64K PTE bits in 64K backed HPTE pages

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  Re: [RFC v6 02/62] powerpc: Free up four 64K PTE bits in 64K backed HPTE pages "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2017-07-20 08:00 +0200

#1692461 — Re: [RFC v6 02/62] powerpc: Free up four 64K PTE bits in 64K backed HPTE pages

Ram Pai <linuxram@us.ibm.com> writes:

> Rearrange 64K PTE bits to  free  up  bits 3, 4, 5  and  6
> in the 64K backed HPTE pages. This along with the earlier
> patch will  entirely free  up the four bits from 64K PTE.
> The bit numbers are  big-endian as defined in the  ISA3.0
>
> This patch  does  the  following change to 64K PTE backed
> by 64K HPTE.
>
> H_PAGE_F_SECOND (S) which  occupied  bit  4  moves to the
> 	second part of the pte to bit 60.
> H_PAGE_F_GIX (G,I,X) which  occupied  bit 5, 6 and 7 also
> 	moves  to  the   second part of the pte to bit 61,
>        	62, 63, 64 respectively
>
> since bit 7 is now freed up, we move H_PAGE_BUSY (B) from
> bit  9  to  bit  7.
>
> The second part of the PTE will hold
> (H_PAGE_F_SECOND|H_PAGE_F_GIX) at bit 60,61,62,63.
> NOTE: None of the bits in the secondary PTE were not used
> by 64k-HPTE backed PTE.
>
> Before the patch, the 64K HPTE backed 64k PTE format was
> as follows
>
>  0 1 2 3 4  5  6  7  8 9 10...........................63
>  : : : : :  :  :  :  : : :                            :
>  v v v v v  v  v  v  v v v                            v
>
> ,-,-,-,-,--,--,--,--,-,-,-,-,-,------------------,-,-,-,
> |x|x|x| |S |G |I |X |x|B| |x|x|................|x|x|x|x| <- primary pte
> '_'_'_'_'__'__'__'__'_'_'_'_'_'________________'_'_'_'_'
> | | | | |  |  |  |  | | | | |..................| | | | | <- secondary pte
> '_'_'_'_'__'__'__'__'_'_'_'_'__________________'_'_'_'_'
>
> After the patch, the 64k HPTE backed 64k PTE format is
> as follows
>
>  0 1 2 3 4  5  6  7  8 9 10...........................63
>  : : : : :  :  :  :  : : :                            :
>  v v v v v  v  v  v  v v v                            v
>
> ,-,-,-,-,--,--,--,--,-,-,-,-,-,------------------,-,-,-,
> |x|x|x| |  |  |  |B |x| | |x|x|................|.|.|.|.| <- primary pte
> '_'_'_'_'__'__'__'__'_'_'_'_'_'________________'_'_'_'_'
> | | | | |  |  |  |  | | | | |..................|S|G|I|X| <- secondary pte
> '_'_'_'_'__'__'__'__'_'_'_'_'__________________'_'_'_'_'
>
> The above PTE changes is applicable to hugetlbpages aswell.
>
> The patch does the following code changes:
>
> a) moves  the  H_PAGE_F_SECOND and  H_PAGE_F_GIX to 4k PTE
> 	header   since it is no more needed b the 64k PTEs.
> b) abstracts  out __real_pte() and __rpte_to_hidx() so the
> 	caller  need not know the bit location of the slot.
> c) moves the slot bits the secondary pte.
>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
With changes suggested for the first patch.

> Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> ---


-aneesh

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