get_user_pages() and shared memory question

[Timur Tabi]

Hi,

Is it possible for a page of memory that's been "grabbed" with get_user_pages() to ever be 
allocated to another process?  I'm assuming the answer is no, but I have a specific case I 
want to ask about.

Let's say an application allocates some shared memory, and then calls into a driver which 
calls get_user_pages().  The driver exits without releasing the pages, so they now have a 
reference count on them.  Then the application deallocates the shared memory.  At this 
point, the virtual addresses disappear, and no process owns them, but the pages still have 
a reference count.

Another process now tries to allocate a shared memory buffer.  Is there any way that this 
new buffer can contain those pages that were grabbed with get_user_pages() (i.e. that 
already have a reference count)?

Until 2.6.7, there was a bug in the VM where a page that was grabbed with get_user_pages() 
could be swapped out.  Those of you familar with the OpenIB work know what I'm talking 
about.  Would that bug affect anything I'm talking about?

--
Timur Tabi
Staff Software Engineer
timur.tabi@xxxxxxxxxxx

One thing a Southern boy will never say is,
"I don't think duct tape will fix it."
     -- Ed Smylie, NASA engineer for Apollo 13
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