linux-kernel - [Help] : RSS/PSS showing 0 during smaps for Xorg

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Message-ID: <1327313719.76517.YahooMailNeo@web162002.mail.bf1.yahoo.com>
Date:	Mon, 23 Jan 2012 02:15:19 -0800 (PST)
From:	PINTU KUMAR <pintu_agarwal@...oo.com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: [Help] : RSS/PSS showing 0 during smaps for Xorg

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.

Thanks.

With Regards,
Pintu
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