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.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>