bug#46881: 28.0.50; pdumper dumping causes way too many syscalls

[Alan Third]

On Tue, Mar 02, 2021 at 08:45:04PM +0000, Pip Cet wrote:
> On Tue, Mar 2, 2021 at 8:35 PM Pip Cet <pipcet@gmail.com> wrote:
> > I've looked into the problem, and it seems easy to solve and worth it
> > in terms of debuggability and performance.
> 
> Very rough benchmarks, but this seems to be clearly worth it:
> 
> Performance:
> With patch:
> real    0m3.861s
> user    0m3.776s
> sys    0m0.085s
> 
> Without patch:
> real    0m7.001s
> user    0m4.476s
> sys    0m2.511s
> 
> Number of syscalls:
> With patch: 415442
> Without patch: 2028307

My quick test on macOS by doing:

rm src/*.pdmp
time make

sees it going from ~26s without patch to ~10s with patch, so a
considerable improvement.

> > Patch will be attached once this has a bug number.
> 
> And here's the patch. Testing would be very appreciated.

It appears to work fine here, but I don't know if there's anything
specific to test other than just running Emacs.
-- 
Alan Third