* Is the address space of a process continous
@ 2005-12-04 21:37 Mohamed El Dawy
2005-12-04 21:46 ` Arjan van de Ven
0 siblings, 1 reply; 2+ messages in thread
From: Mohamed El Dawy @ 2005-12-04 21:37 UTC (permalink / raw)
To: linux-kernel
Hi,
I have a question. In the vma_memory_address struct, there are 2
fields "vm_start" and "vm_end". I was wondering, does the process
address space include all addresses between those 2 addresses? or
could there be holes inside this range?
The main reason I am asking is because I tried to call __follow_page()
on some of those addresses and got NULL as a result. I am not sure if
this is a hole, or just a problem with my code!
Thanks a lot in advance
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Is the address space of a process continous
2005-12-04 21:37 Is the address space of a process continous Mohamed El Dawy
@ 2005-12-04 21:46 ` Arjan van de Ven
0 siblings, 0 replies; 2+ messages in thread
From: Arjan van de Ven @ 2005-12-04 21:46 UTC (permalink / raw)
To: Mohamed El Dawy; +Cc: linux-kernel
On Sun, 2005-12-04 at 15:37 -0600, Mohamed El Dawy wrote:
> Hi,
> I have a question. In the vma_memory_address struct, there are 2
> fields "vm_start" and "vm_end". I was wondering, does the process
> address space include all addresses between those 2 addresses? or
> could there be holes inside this range?
>
> The main reason I am asking is because I tried to call __follow_page()
> on some of those addresses and got NULL as a result. I am not sure if
> this is a hole, or just a problem with my code!
the kernel does this on demand; eg
user mmaps a range
user touches (read or writes) part of that range
each time the user gets to a page that wasn't touched/used before, the
kernel takes a fault and fills in the address.
if you get nulls it's just pages that haven't been used yet.
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