Re: [Qemu-devel] [PATCH] oslib: make error handling more reasonable

[Daniel P. Berrange]

On Tue, Feb 14, 2012 at 12:42:58PM +0000, Paul Brook wrote:
> > > abort can create core dumps or start a debugger which is
> > > useful for me and maybe other developers, too.
> > 
> > I consider abort() on OOM somewhat eccentric.  abort() is for
> > programming errors.  Resource shortage is an environmental error that is
> > sometimes (but not always) caused by a programming error.
> > 
> > I'd rather inconvenience programmers (by making it a little bit harder
> > to debug programming errors that cause OOM) than confuse users with
> > inappropriate scary "crashes".
> 
> While I agree that abort() is not the most friendly failure method, I don't 
> tthink it's worth trying to handle OOM gracefully.  Once we hit OOM I'd say 
> we're pretty much beyond hope.  The best thing we can do is exist as quickly 
> as possible.  For the vast majority of systems there isn't any reason to 
> believe things will somehow get better if we try again later.
> 
> Initial guest RAM allocation is maybe a special case worth a polite error.  
> OTOH if you're near the limit then there's a fair chance the -m allocation 
> will succeed, but some later allocation will not.
> 
> The only way to handle this rebustly is to pre-allocate all the memory we're 
> ever going to need[1].  I don't see that happening.

FWIW, users can already opt-in to pre-allocation if running KVM enabled QEMU

   -mem-path /dev/shm  -mem-prealloc   (or /dev/hugepages more usefully)

Regards,
Daniel
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