linux-kernel - Re: [RFC v2 02/12] powerpc: Free up four 64K PTE bits in 64K backed hpte pages.

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Date:   Tue, 20 Jun 2017 16:25:07 -0700
From:   Ram Pai <linuxram@...ibm.com>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        dave.hansen@...el.com, paulus@...ba.org,
        aneesh.kumar@...ux.vnet.ibm.com
Subject: Re: [RFC v2 02/12] powerpc: Free up four 64K PTE bits in 64K backed
 hpte pages.

On Tue, Jun 20, 2017 at 04:21:45PM +0530, Anshuman Khandual wrote:
> On 06/17/2017 09:22 AM, Ram Pai wrote:
> > 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.
> > 
> > This patch does the following change to 64K PTE that is
> > backed by 64K hpte.
> > 
> > H_PAGE_F_SECOND which occupied bit 4 moves to the second part
> >         of the pte.
> > H_PAGE_F_GIX which  occupied bit 5, 6 and 7 also moves to the
> >         second part of the pte.
> > 
> > since bit 7 is now freed up, we move H_PAGE_BUSY from bit 9
> > to bit 7. Trying to minimize gaps so that contiguous bits
> > can be allocated if needed in the future.
> > 
> > The second part of the PTE will hold
> > (H_PAGE_F_SECOND|H_PAGE_F_GIX) at bit 60,61,62,63.
> 
> I still dont understand how we freed up the 5th bit which is
> used in the 5th patch. Was that bit never used for any thing
> on 64K page size (64K and 4K mappings) ?

yes. it was not used. So I gladly used it :-)


RP