Re: scratch/hash-table-perf 2d28042f56a 19/35: Use non-Lisp allocation for internal hash-table vectors

Re: scratch/hash-table-perf 2d28042f56a 19/35: Use non-Lisp allocation for internal hash-table vectors

[Dmitry Gutov]

On 04/01/2024 17:56, Mattias Engdegård wrote:
> +/* Like xmalloc, but makes allocation count toward the total consing.
> +   Return NULL for a zero-sized allocation.  */
> +void *
> +hash_table_alloc_bytes (ptrdiff_t nbytes)
> +{
> +  if (nbytes == 0)
> +    return NULL;
> +  tally_consing (nbytes);
> +  return xmalloc (nbytes);
> +}

Sorry if it's a stupid question, but if the operation doesn't add any 
Lisp "garbage", why increase the consing counter? That is likely 
triggers more GCs earlier which otherwise might not run, and if there 
are no slots to GC, it seems like they would run in vain.

Re: scratch/hash-table-perf 3e9e68333ae 16/35: Remove rehash-threshold and rehash-size struct members

[Dmitry Gutov]

On 04/01/2024 17:56, Mattias Engdegård wrote:
> branch: scratch/hash-table-perf
> commit 3e9e68333ae15a6544e490851f80da3a8f9ef343
> Author: Mattias Engdegård<mattiase@acm.org>
> Commit: Mattias Engdegård<mattiase@acm.org>
> 
>      Remove rehash-threshold and rehash-size struct members
>      
>      These parameters have no visible semantics and are hardly ever used,
>      so just use the default values for all hash tables.  This saves
>      memory, shrinks the external representation, and will improve
>      performance.

I'm curious whether any of these callers have tested with different 
values and found a difference in performance:

https://github.com/search?q=%3Arehash-threshold+language%3A%22Emacs+Lisp%22&type=code&l=Emacs+Lisp