memory profiling question

Hi,

I'm seeing something I don't understand while doing
a memory profile of a program:

io.b:17	262652	262728			n := sys->read(fd, buf[nr:], nb-nr);

It seems that this line is responsible for 262k (in use),
however, this is just reading into a slice.

Something similar seem to happen to some lines that
allocate file descriptors that are out of scope (allocated
within a function, then the function returns after reading
something). mprof says such lines still hold some memory,
but I don't see how they could.

Most of the memory seems to come from the main pool.

This is on macos, using this version
Inferno Fourth Edition (20070901) main (pid=20503) interp

Anyone else saw something similar or can tell
me what I'm missing?

thanks a lot