question on memory map cleanup stuff

question on memory map cleanup stuff

[Chris Friesen]

I've got a small feature that maps a page of kernel memory to userspace via a 
syscall, then uses that page for various things.

Currently, I'm marking the page reserved, then exporting it via 
remap_page_range().  This means that I need to clean up my mapping whenever the 
memory map is destroyed (process death, exec(), daemonize, etc.).

It appears that I should be able to put my cleanup code in exit_mmap().  Since 
the cleanup code calls do_munmap() on the address, I would want to call it 
before taking mm->page_table_lock, correct?

Also, normally I would hold mm->mmap_sem before calling do_munmap().  Would I 
still need this if I'm calling it from exit_mmap()?  Presumably nobody else can 
get at it anymore...

Thanks,

Chris

Re: question on memory map cleanup stuff

[William Lee Irwin III]

On Mon, Oct 18, 2004 at 04:57:20PM -0600, Chris Friesen wrote:
> I've got a small feature that maps a page of kernel memory to userspace via 
> a syscall, then uses that page for various things.
> Currently, I'm marking the page reserved, then exporting it via 
> remap_page_range().  This means that I need to clean up my mapping whenever 
> the memory map is destroyed (process death, exec(), daemonize, etc.).
> It appears that I should be able to put my cleanup code in exit_mmap().  
> Since the cleanup code calls do_munmap() on the address, I would want to 
> call it before taking mm->page_table_lock, correct?
> Also, normally I would hold mm->mmap_sem before calling do_munmap().  Would 
> I still need this if I'm calling it from exit_mmap()?  Presumably nobody 
> else can get at it anymore...

vma->vm_ops->close() often suffices for such without disturbing the core.


-- wli

Re: question on memory map cleanup stuff

[Chris Friesen]

William Lee Irwin III wrote:

> vma->vm_ops->close() often suffices for such without disturbing the core.

Ah.  That looks promising.

Thanks.

Chris

Re: question on memory map cleanup stuff

[Chris Friesen]

William Lee Irwin III wrote:
> On Mon, Oct 18, 2004 at 04:57:20PM -0600, Chris Friesen wrote:
> 
>>I've got a small feature that maps a page of kernel memory to userspace via 
>>a syscall, then uses that page for various things.
>>Currently, I'm marking the page reserved, then exporting it via 
>>remap_page_range().  This means that I need to clean up my mapping whenever 
>>the memory map is destroyed (process death, exec(), daemonize, etc.).

> vma->vm_ops->close() often suffices for such without disturbing the core.

I'm running into a problem.

At the time of close(), I need to figure out which page to unreserve and free. 
However, when I call

follow_page(vma->vm_mm, vma->vm_start, 0);

it returns zero. How do I go from vma to page?

Chris

Re: question on memory map cleanup stuff

[William Lee Irwin III]

William Lee Irwin III wrote:
>> vma->vm_ops->close() often suffices for such without disturbing the core.

On Tue, Oct 19, 2004 at 12:19:00PM -0600, Chris Friesen wrote:
> I'm running into a problem.
> At the time of close(), I need to figure out which page to unreserve and 
> free. However, when I call
> follow_page(vma->vm_mm, vma->vm_start, 0);
> it returns zero. How do I go from vma to page?

You generally need to keep track of this yourself, as during ->close()
the pagetables have already been destroyed. linear_page_index() can
tell you the offset into the object the vma maps, but ultimately, you
have to track the pages yourself. vma->vm_private_data can be used to
attach various accounting structures to the vma.


-- wli