When Are Free Pages Zeroed?

When Are Free Pages Zeroed?

[Patrick Simmons]

I'm looking into the Linux memory management subsystem and need to know 
when freed pages are zeroed.  Specifically, are they zeroed just before 
they are reallocated, immediately after they are freed, or sometime 
in-between?  Also, what files/functions would I need to modify to change 
this behavior?

Thanks for any help and kindest regards,
--Patrick

-- 
If I'm not here, I've gone out to find myself.  If I get back before I return, please keep me here.

When Are Free Pages Zeroed?

[Mulyadi Santosa]

Hi patrick :)

On Thu, Nov 10, 2011 at 14:43, Patrick Simmons
<linuxrocks123@netscape.net> wrote:
> I'm looking into the Linux memory management subsystem and need to know
> when freed pages are zeroed. ?Specifically, are they zeroed just before
> they are reallocated, immediately after they are freed, or sometime
> in-between? ?Also, what files/functions would I need to modify to change
> this behavior?

I vaguely recall that zeroing is done in (re)-allocation. Thus, during
freeing pages, you just mark it as free and let the allocator handle
it further (perhaps doing block combining--forgot the technical name).

The function that does allocation while zeroing IIRC is kzalloc.


PS: IIRC too, once zero-ing isn't done anywhere. But later, it is
found that it could be a security issue since it might leak sensitive
data.


-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com