Atop man page for mwrit NFS metric is confusing

[gleventhal]

Good day Gerlof (et. al.),

I believed that when the man page said:

the num‐
            ber of bytes written via memory mapped I/O pages ('mwrit').

That it was referring to mmap(2)-ed files which reside on NFS being written-out, because that's what I often think memory mapped IO means (mmap).

Some other stats, and the knowledge that a given application wasn't using mmap led me to question this assumption, and as I understand, the "mwrit" value comes from the 8th field of the /proc/pid/mountstats line that begins with "bytes:" which would be the "NFSIOS_WRITEPAGES"[0] metric used by the Linux kernel.

[0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/nfs_iostat.h#n70

As I understand, that metric is simply a counter of pages involved with a given write of any NFS-based file and is orthogonal to mmap(2).

Perhaps you already know this, and I've simply misunderstood your intention the man page, or there is some other mistake, but could you please clarify, and ideally make the man page more explicit in this regard?

Once again, big fan of atop, it's great stuff. Cheers!

Regards, Gregg Leventhal