Re: Turning on Sparsemem

[Dave Hansen <dave@linux.vnet.ibm.com>]

On Tue, 2008-08-05 at 15:04 -0700, C Michael Sundius wrote:
> still that code is strange to me:
> 
> -------------code
> static inline struct mem_section *__nr_to_section(unsigned long nr)
> {
>         if (!mem_section[SECTION_NR_TO_ROOT(nr)])
>                 return NULL;
>         return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
> }
> 
> --------------
> 
> on the first line of the function above, what does it mean "if not 
> <struct>"?  seems that returns true if
> the contents of that struct is "0"... but either way, doesn't that have 
> to be initialized to something before
> it is called from memory_present()?

Yeah, this is confusing code.  The goal here was to not have any #ifdefs
for the normal vs. extreme cases.  In the !EXTREME case, the
mem_section[] array is statically allocated and that first check gets
optimized out completely.  We check for it, but the compiler kills that
check.  

-- Dave

--
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>