Re: sparsemem support for mips with highmem

[David VomLehn <dvomlehn@cisco.com>]

Christoph Lameter wrote:
> Randy Dunlap wrote:
>
> > +Sparsemem divides up physical memory in your system into N section of M
> >
> >                                                             sections
> >
> > +bytes. Page descriptors are created for only those sections that
> > +actually exist (as far as the sparsemem code is concerned). This allows
> > +for holes in the physical memory without having to waste space by
> > +creating page discriptors for those pages that do not exist.
> >
> >                descriptors
> >
> > +When page_to_pfn() or pfn_to_page() are called there is a bit of overhead to
> > +look up the proper memory section to get to the descriptors, but this
> > +is small compared to the memory you are likely to save. So, it's not the
> > +default, but should be used if you have big holes in physical memory.
> This overhead can be avoided by configuring sparsemem to use a virtual vmemmap
> (CONFIG_SPARSEMEM_VMEMMAP). In that case it can be used for non NUMA since the
> overhead is less than even FLATMEM.
On MIPS processors, the kernel runs in unmapped memory, i.e. the TLB isn't even
used, so I don't think you can use that trick. So, this comment doesn't apply to
all processors.