Re: [PATCH v2] MIPS64: Support of at least 48 bits of SEGBITS

[Leonid Yegoshin]

On 05/15/2015 01:49 PM, David Daney wrote:
> On 05/14/2015 06:34 PM, Leonid Yegoshin wrote:
> > SEGBITS default is 40 bits or less, depending from CPU type.
> > This patch introduces 48bits of application virtual address (SEGBITS) 
> > support.
> > It is defined only for 16K and 64K pages and is optional (configurable).
> >
> > Penalty - a small number of additional pages for generic (small) 
> > applications.
> > But for 64K pages it adds 3rd level of PTE structure, which has a little
> > impact during software TLB refill.
> >
> > This patch is needed because MIPS I6XXX and P6XXX cores have 48 bit of
> > virtual address in each segment (SEGBITS).
>
> Those processors don't require the patch.  You wrote the patch to give 
> a larger VA space at the request of kernel users.  So perhaps say:
>
>   The patch (optionally) increases the VA space available to userspace 
> processes from N-bits to 48-bits

... if CPU model supports that

> > +config 48VMBITS
>
> Should probabaly be called VABITS instead of VMBITS to match the terms 
> used in the architecture reference manuals, as well as other ports 
> (ARM64).
>
> Perhaps MIPS_VA_BITS_48

I don't mind here. It can be even called 48SEGBITS or so, to match arch 
manual more. MIPS Arch manual never says about VA bits but speaks about 
PABITS and SEGBITS.

- Leonid.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/