RE: How to make Linux scale up WRT bandwidth and size?

Jeremy Fitzhardinge (
Thu, 29 Apr 1999 13:55:24 -0700 (PDT)

On 29-Apr-99 Alex Buell wrote:
> On Thu, 29 Apr 1999, Jeremy Fitzhardinge wrote:
>> You can't mmap block devices. I don't think avoiding the filesystem
>> will help particularly, though you could avoid some filesystem
>> overhead in the real-time path by preallocating the file.
> How come I can mmap() /dev/zero ?

For one, /dev/zero is a character device. It's also specifically designed to be
mmaped, and is very simple to mmap because there's no real underlying device.

There's no fundimental reason why a block device can't be mmaped, but there are
a number of implementation gotchas, pariticularly on 32 bit machines.


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