Date: Mon, 13 Jun 2005 15:03:10 +0000 From: "Apache Xie" <apachexm@hotmail.com> To: tinguely@casselton.net Cc: freebsd-hackers@freebsd.org Subject: Re: contigmalloc() and mmap() Message-ID: <BAY19-F577FE4F7712233B4F5BFAC4F00@phx.gbl> In-Reply-To: <200506131241.j5DCfXL5026935@casselton.net>
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>From: Mark Tinguely <tinguely@casselton.net> >To: apachexm@hotmail.com, 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? _________________________________________________________________ Express yourself instantly with MSN Messenger! Download today it's FREE! http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/
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