[EMAIL PROTECTED] (Joseph H. Buehler) writes:
> [EMAIL PROTECTED] (Anand Palaniswamy) writes:
>
> > Another bad side effect of this limitation is that the famous "return
> > memory to OS" bug can not be implemented on Linux (ie, there is no
> > heap "shrinking").
>
> Are you sure about that? I use GNU emacs a lot and just tried an
> experiment on a machine running RedHat because I have observed address
> space shrinking on other UNIX's. Sure enough, the "ps" command under
> RedHat reports that the emacs process size increases when it reads a
> big file, but decreases back to what it was when I kill the buffer. I
> don't mean the resident size, either, but the overall process address
> space size.
It is possible to unmap memory and return it to the OS on Linux. I am
sure Emacs does that. The classic VM garbage collector can not do
that. It wants to keep the memory mapped (so it can always be sure
that the heap is contiguous -- unmmapping might lead to someone else
stealing the part you just unmapped). The trick classic VM uses on
Solaris and on Windows is to keep the heap mapped but not have any
swap committed to it (which is slightly different from completely
unmapping it).
Emacs can probably deal with discontiguous heaps. (Infact I wouldn't
be surprised if there is a special heap for large files).
-Anand.
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