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SubjectRe: [Help] : RSS/PSS showing 0 during smaps for Xorg
________________________________
>From: Hugh Dickins <hughd@google.com>
>To: PINTU KUMAR <pintu_agarwal@yahoo.com>
>Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>; "linux-mm@kvack.org" <linux-mm@kvack.org>
>Sent: Tuesday, 24 January 2012 1:01 AM
>Subject: Re: [Help] : RSS/PSS showing 0 during smaps for Xorg
>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
>

Dear Mr. Hugh,
 
Thank you very much for your reply.
Is there a way to convert our mapped pages to a normal pages. I tried pfn_to_page() but no effect.
I mean the page is considered normal only if it is associated with "struct page" right???
Is is possible to convert these pages to a normal struct pages so that we can get the Rss/Pss value??
 
Also, the VM_PFNMAP is being set for all dirvers during remap_pfn_range and stills shows Rss/Pss for other drivers.
Then why it is not shown for our driver?
How to avoid remap_pfn_range to not to set VM_PFNMAP for our driver?
 
Please let me know.
 
 
 
Thanks, Regards,
Pintu
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