Re: [PATCH] Enhance _Hashtable for range insertion 0/5

[Jonathan Wakely <jwakely@redhat.com>]

On Mon, 20 Jun 2022 at 17:58, François Dumont via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> Hi
>
> Here is a series of patch to enhance _Hashtable behavior mostly in the
> context of range insertion. I also start considering the problem of
> memory fragmentation in this container with 2 objectives:
>
> - It is easier to find out when you're done with the elements of a
> bucket if the last node of the bucket N is the before-begin node of
> bucket N + 1.
>
> - It is faster to loop through nodes of a bucket if those node are close
> in memory, ultimately we should have addressof(Node + 1) ==
> addressof(Node) + 1

Have these changes been profiled or benchmarked? Is it measurably
faster? By how much?


> [1/5] Make more use of user hints as both insertion and allocation hints.
>
> [2/5] Introduce a new method to check if we are still looping through
> the same bucket's nodes
>
> [3/5] Consider that all initializer_list elements are going to be inserted
>
> [4/5] Introduce a before-begin cache policy to remember which bucket is
> currently pointing on it
>
> [5/5] Prealloc nodes on _Hashtable copy and introduce a new assignment
> method which replicate buckets data structure
>
> François
>