10k files inside a single folder is not a problem on Ext4. It should have the dir_index option enabled by default, which indexes directories content using a btree-like structure to prevent performance issues.

#!/bin/bash
while [ true ]; 
do mkdir ~/`cat /dev/urandom | tr -cd a-zA-Z | head -c 15`
done

#!/bin/bash
while [ true ]; 
do mkdir ~/`cat /dev/urandom | tr -cd a-zA-Z | head -c 15`
done

#!/bin/bash
while [ true ]; 
do mkdir ~/`cat /dev/urandom | tr -cd a-zA-Z | head -c 15`
done