[dpdk-dev] DDPK use of MAP_FIXED in mmap

[Neil Horman]

On Mon, Dec 08, 2014 at 07:02:38PM +0000, Karmarkar Suyash wrote:
> Hello,
> 
> In DPDK when we use mmap why are we passing the MAP_FIXED flag when Linux man page itself says that the option is discouraged? Any specific reason for passing the MAP_FIXED flag?
> 
Because theres nothing wrong with doing so.  The man page says its discouraged
because it creates less portable applications (due to the fact that not all
operating systems support MAP_FIXED).  Given that we currently only support BSD
and Linux however, and given that MAP_FIXED was added to POSIX for
XSI compliant systems, it seems like a reasonable thing to use, as we will most
likely never run into a system that won't support it
Neil

> 
> http://linux.die.net/man/2/mmap
> 
> MAP_FIXED
> Don't interpret addr as a hint: place the mapping at exactly that address. addr must be a multiple of the page size. If the memory region specified by addr and len overlaps pages of any existing mapping(s), then the overlapped part of the existing mapping(s) will be discarded. If the specified address cannot be used, mmap() will fail. Because requiring a fixed address for a mapping is less portable, the use of this option is discouraged.
> 
> 
> Regards
> Suyash Karmarkar
>