Kamal R. Prasad wrote this message on Sun, Dec 05, 2004 at 00:38 +0530:
> I wrote an mmap() interface for a USB device. But when I made a call to
> it using mmap(), I saw that mmap interface is called 3-4 times. The
> calls are being made from within mmap() i.e. sys/vm/vm_mmap.c. Can
> someone tell me if there is something like a re-try going on for some
> reason?
> From userspace, I called it as
> addr = mmap(NULL, 1024, PROT_READ, MAP_SHARED, fd, 0);
> The version of OS is Freebsd 5.3(stable).
each mmap call will be called whenever the kernel needs to map that
specific page.. say you map 16k of your device... it won't map any
of the 16k until the first time it is accessed, then it will call the
mmap routine for each page as it is accessed... it is also possible that
memory for the mappings needs to be reclaimed, at which point those page
mappings will be reaped, and your mmap function will be called again when
they need to be accessed again..
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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