Ignat Korchagin from Cloudflare has created a patch to improve the performance of dm-crypt considerably, see https://github.com/cloudflare/linux
It seems they run this patch themself in over 200 datacenters. And he has today initiated actions to get the patch included in the upstream, see https://lkml.org/lkml/2020/6/19/1934 Perhaps the Debian-kernel maintainers would consider creating a 5.4 amd64 kernel-package with this patch implemented. Just as *linux-image-5.4.0-0.bpo.4-amd64* package in buster-backports repository. In the light of SEDs (self-encrypting drives) the latest years have turned out to be less secure than expected, dm-crypt is more relevant than ever ;-) Best regards Brian Wengel, Denmark