On Mon, 23 Jan 2012, PINTU KUMAR wrote:

Dear All,

I am facing one problem for one of my kernel module for our linux mobile with kernel2.6.36.

When I do cat /proc/<Xorg pid>/smaps | grep -A 11 /dev/ump , to track information for my ump module,
we always get Rss/Pss as 0 kB as shown below:
cat /proc/1731/smaps | grep -A 11 /dev/ump
414db000-415ff000 rw-s 00015000 00:12 6803       /dev/ump
Size:               1168 kB
Rss:                   0 kB
Pss:                   0 kB
track_rss_value = 0, iswalkcalled = 1, smap_pte_range_called = 1, swap_pte = 0, not_pte_present = 0, not_normal_page = 1
isspecial = 0, not_special = 1, isMixedMap = 0, pfnpages_null = 0, pfnoff_flag = 0, not_cow_mapping = 1, normal_page_end = 0
 
After tracing down the problem, I found out that during "show_smaps" in fs/proc/task_mmu.c and during call to smaps_pte_range the vm_normal_page() is always returning NULL for our /dev/ump driver.
(smaps_pte_range() is the place where Rss/Pss information is populated)
Thus mss->resident (Rss value) is never getting incremented.  
 
To trace the problem I added few flags during show_smaps & vm_normal_page() as shown above. The value of 1 indicates that the condition is executed.
Thus "normal_page_end" indicates that the "vm_normal_page" has never ended successfully and always returns from 
"!is_cow_mapping()".
 
So, I wanted to know the main cause for vm_normal_page() always returning NULL page for our ump driver. 
What is that I am missing in my driver ?
 
Can anyone please let me know what could be the problem in our driver.

This not evidence of any problem in your driver.

vm_normal_page() returns NULL because the pages mapped by your driver
are not normal faultable and reclaimable pages, but an area of physical
memory mapped in by remap_pfn_range(), which sets the VM_PFNMAP flag.

The mm subsystem does not count such pages towards rss (or pss),
hence your 0s.

Hugh

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