get_user_pages question

[Eli Cohen]

Hi,
I have been tryin to use get_user_pages() on malloced memory and get the 
list of pages but it does not work as
I expected:
1. malloc a buffer in user space
2. issue ioctl, invoke get_user_pages() and save the page descriptors I 
obtained.
3. at a later time, issue another ioctl, invoke get_user_pages() again 
and save another copy of the page descriptors.
4. Compare the two lists of page descriptors. They're not all the same.

Apparently some pages were discarded and the subsequent page fault 
brought a new page. I expected the original page to be in the swap cache 
and get the old page again. I repeated the experiment but before the 
first ioctl I wrote something to all the pages but got the same results. 
I used 2.4.21-4 (RH AS 3.0).

Can anyone clarify?
thanks
Eli
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