mmap(2) maps a file to a range of memory and gives
the calling process a
void* to manipulate the contents
of the file. If no file descriptor is given, it creates an
“anonymous” memory range. In both cases, the memory range
can be used for inter-process communication.
As an additional feature, the caller can specify how child processes
see the memory. If
MAP_INHERIT is set, the children
see the same as the parent. If additionally (or more precisely OR-ally)
MAP_PRIVATE is set, modifications (i.e. writes) by the parent are
invisible to the children. If
MAP_SHARE is set, the
children see the bytes written by the parent. The
syscall allows setting these bits for arbitrary pages.
Now, what would be the most stressing situation for the kernel?
Overlapping memory ranges with different copy/share policies for
several generations of processes. This program does exactly that.
It subdivides the same piece of memory recursively, and each child
sets another inheritance policy on top of the set ones of the stack
stress.mmap [-f file] [-m size] [-r level] [-n num]
-f <file> use <file> to mmap on
-m <size> size of mmaped area in bytes
-r <level> the number of recursions
-n <num> number of byteblocks to touch in each incarnation
TODO: let each child
mmap the same file to another location,
with different policies…