On Thursday, 11 April 2024 at 00:24:44 UTC, Andy Valencia wrote:
I wrote a "count newlines" based on mapped files. It used
about twice the CPU of the version which just read 1 meg at a
time. I thought something was amiss (needless slice
indirection or something), so I wrote the code in C. It had
the same CPU usage as the D version. So...mapped files, not so
much. Not D's fault. And writing it in C made me realize how
much easier it is to code in D!
[...]
The setup of a memory mapped file is relatively costly. For
smaller files it is a net loss and read/write beats it hands
down. Furthermore, sequential access is not the best way to
exploit the advantages of mmap. Full random access is the strong
suite of mmap as it replaces kernel syscalls (lseek,read, write
or pread, pwrite) by user land processing.
You could try MAP_POPULATE option in the mmap as it enables
read-ahead on the file which may help on sequential code.
