From: Mark Tinguely <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED], freebsd-hackers@freebsd.org
Subject: Re: contigmalloc() and mmap()
Date: Mon, 13 Jun 2005 07:41:33 -0500 (CDT)
> I browsed kernel tree, I found those drivers which use contigmalloc()
and
> contigfree() always call these two kernel interfaces in _attach() and
> _detach(), but in my driver, I call contigmalloc() in ioctl(), and call
> contigfree() in a callout function which is set by callout_reset().
> What I want to know is if contigmalloc() and contigfree() can only be
used
> under some conditions?
Allocating early prevents unfullfilled requests due to fragmentation of
the physical memory. I believe starting in FreeBSD 5.x, contigmalloc()
started to fill physical memory requests from the higher memory locations
to help with fragmentation. FreeBSD 5/6 has a Unified Meory Allocator
that helps allocate/free cycles.
> And recently, I modified my driver, I allocated a big chunk of
contiguous
> physical memory using contigmalloc() in the driver's _attach()
function,
> and I use a simple first-fit algorithm to manage this memory myself,
which
> mean in ioctl() I use my allocate/deallocate functions instead of
> contigmalloc(),
> in _detach() function contigfree() is called to free the big chunk of
> memory,
> no panic again, but sometimes, process cannot get the correct data from
> the mmaped memory. I don't know why.
Are you sure that you are allocating page length request on page
boundaries?
Are you checking the success/failure of the allocation? Your page faults
before implementing your own allocation sounds like you did not check
the return status from contigmalloc() and were dereferencing a pointer
on page 0.
--Mark Tinguely.
I checked the return values of those functions in my code, the problem
I meet now seems caused by some cache coherency, I am still not sure,
maybe I should do some more tests.
And I used /dev/mem and bktr driver as the template when I was porting
my driver, the platform I use is IA-64, in sys/ia64/ia64/mem.c, I find this
line:
*paddr = IA64_PHYS_TO_RR7(offset);
why return the region 7 address?
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