On Tue, Aug 9, 2022, 9:43 AM Po Lu <luangruo@yahoo.com> wrote:

> Lynn Winebarger <owinebar@gmail.com> writes:
>
> > I'm not sure you can conclude that the benefit would be minor when the
> > non-collected space is a 184MB dump file instead of a fixed pure space
> > that is 2 or 2.4MB as it is in the standard pdump.
>
> AFAIK we don't officially support any non-standard dump.
>

I'm not sure how that's relevant, but depending on what you mean by
"support", it may not be totally accurate.  Aside from providing the option
of including site-load and site-init in the system build, there is the
user-level function dump-emacs-portable.   It's accurate to say the
maintainers are not responsible for supporting every random set of
libraries put together in a dump.  But it's also fair to say that the
impact of the system design on nonstandard user dumps is within the remit
of the maintainers as a general matter.  That said, the priority of such
concerns is entirely up to the maintainers.


> At least some vestiges of the write barrier appear to be in place
> > during dump mode.  I've had to make a lot of minor corrections of
> > "defconst" keymaps to defvar, for example due to pure_write_error
> > getting called.  Whether that barrier is uniformly enforced or not is
> > one of the reasons I suspect this quick hack would not be sufficient.
>
> I don't think it's very well enforced.  For example, any C code that
> calls XSETCAR without checking whether or not the object (i.e. the reuse
> argument to Fmatch_end) is writable will result in the invariant being
> broken.
>

True, but if all relevant mutators are effectively contained in lisp.h, the
problem of imposing a write barrier would be effectively contained.  Then
it would just be a matter of determining if the cost of the write barrier
being checked at every mutation is paid for by a perceivable reduction in
gc-related pauses.
But as I said, it's just a hack I'm tempted to try.  I probably won't
unless the gc pauses for this mega-dump build become intolerable.

Lynn