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    SubjectRe: [Help] : RSS/PSS showing 0 during smaps for Xorg
    On Mon, 30 Jan 2012, PINTU KUMAR wrote:
    >  
    > >If these are ordinary pages with struct pages, then you could probably
    > >use a loop of vm_insert_page()s to insert them at mmap time, or a fault
    > >routine to insert them on fault.  But as I said, I don't know if this
    > >memory is part of the ordinary page pool or not.
    >  
    > You suggestion about using vm_insert_page() instead of remap_pfn_range worked for me and I got the Rss/Pss information for my driver.

    Oh, I'm glad that happened to work for you.

    > But still there is one problem related to page fault.
    > If I remove remap_pfn_range then I get a page fault in the beginning.
    > I tried to use the same vm_insert_page() during page_fault_handler for each vmf->virtual_address but it did not work.
    > So for time being I remove the page fault handler from my vm_operations.
    > But with these my menu screen(LCD screen) is not behaving properly (I get colorful lines on my LCD).
    > So I need to handle the page fault properly.
    >  
    > But I am not sure what is that I need to do inside page fault handler. Do you have any example or references or suggestions?

    Sounds like you're not using vm_insert_page() properly: I would not expect
    you to get a page fault there once you've set up the area with a loop of
    vm_insert_page()s.

    Check the comments above it in mm/memory.c ("Your vma protection will
    have to be set up correctly" might be relevant).

    Compare how you're using it with other users of vm_insert_page() in
    the kernel tree. Sorry, I don't have time to do your debugging.

    >  
    > >Really, the question has to be, why do you need to see non-0s there?
    > I want Rss/Pss value to account for how much video memory is used by the driver for the menu-screen,Xorg processes.

    So, userspace does an mmap for a large-enough window, but only some part of
    that is filled by the driver (whether by remap_pfn_range or vm_insert_pages),
    and you'd like to communicate back how much via the Rss, instead of adding
    some ioctl or sysfs interface to the driver? Fair enough.

    I expect userspace could also work it out by touching pages of the area
    until it gets a SIGBUS, but that might be too dirty a way of finding out.

    Hmm, SIGBUS: maybe that's related to the faults that are puzzling you:
    perhaps you're mapping less than you need to.

    Hugh
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