Re: [Xen-devel] [PATCH XEN v6 25/32] tools/libs/gnttab: Extensive updates to API documentation.

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Wed, 2015-12-09 at 16:28 +0000, Ian Jackson wrote:
> Ian Campbell writes ("Re: [PATCH XEN v6 25/32] tools/libs/gnttab:
> Extensive updates to API documentation."):
> > On Wed, 2015-12-09 at 16:09 +0000, Ian Jackson wrote:
> > > Is this actually true ?ÂÂNormally close() on an fd does not munmap
> > > anything mmapped from the fd.
> > 
> > Uh yes, I was talking rubbish here, unless the drivers are more magic
> > than
> > I think they are.
> > 
> > So what is the answer? That such memory is wasted and irrecovable until
> > exec?
> 
> I don't know.ÂÂWhat would happen if you munmapped it ?

We discussed all this IRL and concluded after much back and forth that
there is nothing we can do here other than require a call to each relevant
library's _close() method by callers of fork() who do not exec but who care
about the (usually modest) resources consumed by these sorts of mappings.

The _close call after fork should be documented as potentially not actually
achieving anything and we decided to treat this as a future bug if/when it
has a real world impact by fixing.

Ian.

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