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

[Pip Cet]

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

> Patch will be attached once this has a bug number.

And here's the patch. Testing would be very appreciated.

I'm unsure about the precise usage of dump_off vs ptrdiff_t here; I
don't think it matters, but suggestions, nitpicks, and comments, on
this or any other aspect, would be very appreciated.

Pip

0001-Prepare-pdumper-dump-file-in-memory-write-it-in-one-.patch
Description: Text Data