I’ve seen a lot of blog post and issues about the creation of previews and the influence on whole system performance on low machines. As soon as you open a huge picture gallery all worker processes (pm.max_children) gets used to create thumbnails and no processes left to keep the web interface responsive, it looks like the system freeze. I would prefer to keep the frontend usable, even if I have to wait longer for my previews.
Maybe it’s possible to only use a configurable amount/percentage of the processes for thumbnail generation to keep processes free for user interaction.
I think that’s not very hard to implement in a central event handler which checks how many processes hard working before the preview generation gets started.