Re: Should page->count ever be -1?

From: Timur Tabi (ttabi@interactivesi.com)
Date: Wed Jan 03 2001 - 16:59:21 EST

** Reply to message from Andrea Arcangeli <andrea@suse.de> on Wed, 3 Jan 2001
22:55:05 +0100

> > from page_alloc.c (this is 2.2.18pre15). It appears that page->count is
> > already zero when this code is executed, and after it's executed, page->count
> > becomes -1 (or more accurately, 0xFFFFFFFF). Is this acceptable, or is it an
> > error condition?
>
> It's an error condition. Make sure you marked the page as reserved in the mmap
> callback if it's not an mmio region outside RAM.

I mark the page as reserved when I call ioremap and then unmark it after
ioremap returns, but iounmap will fail if it's still reserved (the same line of
code also checks the reserved bit):

         if (!PageReserved(page) && atomic_dec_and_test(&page->count)) {
            ^^^^^^^^^^^^^^^^^^^

Is this what you're saying?

iounmap just calls vfree, which does all the work. However, I'm confused at
this code in vfree:

        vmfree_area_pages(VMALLOC_VMADDR(tmp->addr), tmp->size);
        kfree(tmp);

What's the difference between vmfree_area_pages and kfree? 

-- 
Timur Tabi - ttabi@interactivesi.com
Interactive Silicon - http://www.interactivesi.com

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