Re : Re : sparsemem usage

[moreau francis <francis_moreau2000@yahoo.fr>]

KAMEZAWA Hiroyuki wrote:
> On Thu, 10 Aug 2006 14:46:01 +0000 (GMT)
> moreau francis <francis_moreau2000@yahoo.fr> wrote:
>> Why not implementing page_exist() by simply using mem_map[] ? When
>> allocating mem_map[], we can just fill it with a special value. And
>> then when registering memory area, we clear this special value with
>> the "reserved" value. Hence for flatmem model, we can have:
>>
>> #define page_exist(pfn)        (mem_map[pfn] != SPECIAL_VALUE)
>>  
> putting a special value to a page struct at mem_map + pfn ?

yes

> 
>> and it should work for sparsemem too and other models that will use
>> mem_map[].
>>
>> Another point, is page_exist() going to replace page_valid() ?
> what is page_valid() here ? pfn_valid() (in current kernel) ?

sorry I was meaning pfn_valid() instead of page_valid() in the
whole email.

> 
>> I mean page_exist() is going to be something more accurate than
>> page_valid(). All tests on page_valid() _only_ will be fine to test
>> page_exist(). But all tests such:
>>
>>     if (page_valid(x) && page_is_ram(x))
>>
>> can be replaced by
>>
>>     if (page_exist(x))
>>
>> So, again, why not simply improving page_valid() definition rather
>> than introduce a new service ?
>>

s/page_valid/pfn_valid

> I welcome to do that if implementation is sane.
> pfn_valid() --- check there is a page struct
> page_exist() --- check there is a physical memory.
> 

new definition of pfn_valid() would be "a physical page exists". And
this definition imply the old one "it's safe to read the page struct *"

> but discussing without patch is not very good. please post your patch.
> Then we can discuss more concrete things.
> 

Since I'm not kernel hacker, or rather a newbie one, I try to make sure
that it worth to dig in that direction before working hard to write a
patch.

thanks

Francis



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