anon (a.delete@this.b.com) on January 14, 2020 1:15 am wrote:
> Brendan (btrotter.delete@this.gmail.com) on January 13, 2020 7:21 am wrote:
> > > > This kind of thinking is the reason why the world sucks ("Some software is shit, therefore all software
> > > > should be forced to be shit forever and nobody should ever try to make software better").
> > >
> >
> > Consider a HTTP server - do you want to (e.g.) drop one connection or abort
> > one request, or do you want to get killed and drop all current connections?
> >
> > Consider a word processor - do you want to (e.g.) free memory from the "undo buffer" and retry
> > (and if that doesn't work display a dialog box informing the user and save the current document
> > and shut down gracefully); or do you want to get killed and lose all the user's unsaved work;
> > or do you want kill X11 and screw up every single app that's currently running?
> >
>
> Note that providing the behaviour you asked for here is not possible through virtual memory without overcommit.

It's entirely possible to "munmap()" something when "mmap()" returns ENOMEM.

> The point I was trying to make earlier is that ENOMEM is non-local. You cannot use malloc's return value
> to provide intelligent behavior in out-of-memory situations because you are not guaranteed to get it.

You are guaranteed to increase the chance that you will succeed. Of course you might also be able to re-purpose existing memory (e.g. instead of calling "munmap()" then retrying the "mmap()", do neither and use the existing memory you would've unmapped as the new memory you would've mapped). It's also possible for a kernel to provide a more atomic "unmap then map"; and possible that multiple processes "stealing" recently released memory from each other benefits all processes.

> Instead,
> there's always decent odds that it will be tossed at some background process that you cannot live without
> and which you did not write, and which has no good options for dealing with it.

There's also a small chance that you will be struck by lightning and die tomorrow. If you honestly think that "small chance there's no point trying" is a guarantee of futility then you will quit your job, say goodbye to all your friends and family, then sit in a corner crying for the next several decades.

Alternatively, maybe you could acknowledge that your logic is extremely flawed (acknowledge that "small chance there's no point trying" means "large chance there is a point to trying").

- Brendan