Re: [Help] : RSS/PSS showing 0 during smaps for Xorg

[PINTU KUMAR]

Dear Hugh,
 
Thank you for your help/suggestion so far.
 
Please find further updates on this below.
 
>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.
>perhaps you're mapping less than you need to.

1)  The page fault is not occuring now after calling vm_insert_page() in a loop for every page. The hint about "mapping less than you need to" stricked me. Please check the snapshot below.
     loop
        vm_insert_page(vma,start,page);
        start = start + PAGE_SIZE;
        size = size - PAGE_SIZE;
    until size > 0
 
    I verified other drivers in kernel code and found this is how it is done.
 
2)  But after doing all this also my menu-screen is not proper. Still I am getting colorful lines on the menu-screen.
     Can you point me out what could be the problem??
 
 
 
Thanks, Regards,
Pintu
 
 
>________________________________
>From: Hugh Dickins <hughd@xxxxxxxxxx>
>To: PINTU KUMAR <pintu_agarwal@xxxxxxxxx> 
>Cc: "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>; "linux-mm@xxxxxxxxx" <linux-mm@xxxxxxxxx> 
>Sent: Tuesday, 31 January 2012 12:19 AM
>Subject: Re: [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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