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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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