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

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Date:	Wed, 25 Jan 2012 16:59:41 -0800 (PST)
From:	Hugh Dickins <hughd@...gle.com>
To:	PINTU KUMAR <pintu_agarwal@...oo.com>
cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [Help] : RSS/PSS showing 0 during smaps for Xorg

On Tue, 24 Jan 2012, PINTU KUMAR wrote:
>  
> 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??

I don't understand why you are so anxious to see non-0 numbers there.

I don't know if the pages you are mapping with remap_pfn_range() are
ordinary pages in normal memory, and so already have struct pages, or not.

>  
> Also, the VM_PFNMAP is being set for all dirvers during remap_pfn_range and stills shows Rss/Pss for other drivers.

I'm surprised.  It is possible to set up a private-writable VM_PFNMAP area,
which can then contain ordinary private copies of the underlying pages,
and these copies will count to Rss.  But I thought that was very unusual.

You don't mention which drivers these are that use remap_pfn_range yet
show Rss (and I don't particularly want to spend time researching them).

I can see three or four places in drivers/ where VM_PFNMAP is set,
perhaps without going through remap_pfn_range(): that seems prone
to error, I wouldn't recommend going that route.

> Then why it is not shown for our driver?
> How to avoid remap_pfn_range to not to set VM_PFNMAP for our driver?

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.

Really, the question has to be, why do you need to see non-0s there?

Hugh