I am developing a software based DSM. In order to avoid concurrent
updates on a memory page that is being updated by the runtime I am
using a shadow mapping to perform the updates. This mappings are
created by opening a file, unlinking it and mmap-ing on the file
descriptor. Everything is working but I am experiencing heavy disk I/O
during execution on a machine with a single ext4 file system. Other
machines that use ext3 partitions don't exhibit this behavior (there
is no disk I/O at all). This machine is using the kernel version
2.6.35-25-generic.
The exact steps performed to create the mappings are:
// Create the file
snprintf(tmp, FILENAME_MAX, "/tmp/testXXXXXX");
int fd = mkstemp(tmp);
if(fd < 0) return NULL;
unlink(tmp);
if(ftruncate(fd, count) < 0) {
close(fd);
return NULL;
}
...
// Create a mapping
addr = mmap(NULL, count, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
Does ext4 write to mmap'ed files although they don't have a name in
the file system? Am I doing anything wrong?
Thanks,
Javi
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