swap to a sparse file

[Steve O'Hara-Smith]

On Sat, 13 Oct 2018 14:52:47 +0100
RW via freebsd-questions <freebsd-questions at freebsd.org> wrote:

> On Sat, 13 Oct 2018 08:11:18 +0100
> Steve O'Hara-Smith wrote:
> 
> > On Fri, 12 Oct 2018 19:36:33 +0100
> > RW via freebsd-questions <freebsd-questions at freebsd.org> wrote:
> > 
> > > On Thu, 11 Oct 2018 08:51:14 +0100
> > > Steve O'Hara-Smith wrote:
> > >   
> > > > On Thu, 11 Oct 2018 08:47:05 +0700
> > > > Victor Sudakov <vas at mpeks.tomsk.su> wrote:
> > > >   
> > > > > Is there any good reason I can't just "truncate -s2G /swap0" and
> > > > > make the swap a sparse file?     
> > > > 
> > > > 	Just one - if the space isn't there when the system needs
> > > > it there will be a panic.  
> > > 
> > > Is that really the only reason? I've not paid much attention, but
> > > the warnings I've heard about this have made it sound a lot worse.  
> > 
> > 	There's not much worse the system can do than panic, other
> > than deadlock which might happen if memory needs to be allocated in
> > order to add blocks to the file. IIRC swap on a zvol can deadlock
> > that way.
> 
> 
> Yes, but filling up a drive is relatively avoidable - particularly if
> there's space reserved for root. 

	True enough, although if you are counting on having the space
available then pre-allocating it is a strong guarantee and prevents the
performance penalty of adding a block to a file as an overhead of swapping.

-- 
Steve O'Hara-Smith <steve at sohara.org>