bug#66117: 30.0.50; `find-buffer-visiting' is slow when opening large number of buffers

[Ihor Radchenko <yantar92@posteo.net>]

Ihor Radchenko <yantar92@posteo.net> writes:

> Ihor Radchenko <yantar92@posteo.net> writes:
>
>> The main contributor is set_default_internal. I _suspect_ (because we
>> have non-linear scaling with the number of buffers - 3x increase in the
>> number of files lead to ~6x increase in the run time) that the main
>> contributor here is let-binding `case-fold-search' - special per-buffer
>> variable with no default value.
>
> My suspicion appears to be correct - removing let-binding for
> case-fold-search from `abbreviate-file-name' and
> `inhibit-local-variables-p' made them disappear from the top of the
> reverse call tree.
>
> Then, considering the ubiquity of let-binding case-fold-search across
> Elisp code, speeding up let-binding of special per-buffer variables may
> give us performance boost across Emacs.

What do you think about introducing something like

struct buffer buffer_overrides;

It will be similar to buffer_defaults  in buffer.c, but will hold the
overriding values of buffer-local variables that are to be used instead
of proper buffer-local variables. That way, we can speed up let-binding
of case-fold-search.

-- 
Ihor Radchenko // yantar92,
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