Re: [PATCH 4/4] export: avoid code duplication in include/linux/export.h

[Matthias Maennich]

On Fri, Oct 11, 2019 at 05:31:27PM +0200, Greg Kroah-Hartman wrote:
> On Thu, Oct 10, 2019 at 04:14:43PM +0100, Matthias Maennich wrote:
> > Now that the namespace value is not part of the __ksymtab entry name
> > anymore, we can simplify the implementation of EXPORT_SYMBOL*. By
> > allowing the empty string "" to represent 'no namespace', we can unify
> > the implementation and drop a lot redundant code.  That increases
> > readability and maintainability.
> >
> > As Masahiro pointed out earlier,
> > "The drawback of this change is, it grows the code size. When the symbol
> > has no namespace, sym->namespace was previously NULL, but it is now am
> > empty string "". So, it increases 1 byte for every no namespace
> > EXPORT_SYMBOL. A typical kernel configuration has 10K exported symbols,
> > so it increases 10KB in rough estimation."
>
> 10Kb of non-swapable memory isn't good.  But if you care about that, you
> can get it back with the option to compile away any non-used symbols,
> and that shouldn't be affected by this change, right?

Rasmus suggested to put the 'aMS' flags on the __ksymtab_strings section
to mitigate this:
https://lore.kernel.org/lkml/f2e28d6b-77c5-5fe2-0bc4-b24955de9954@xxxxxxxxxxxxxxxxxx/

I was not yet able to properly test this, so I did not include it in
this series. As I said in the cover letter, this 4th patch might be
optional for 5.4. So, we could defer it to a later time when we have
addressed that properly.

Cheers,
Matthias

> That being said, the code is a lot cleaner, so I have no objection to
> it.
>
> Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>