post install hard drive thrashing, slow boot

[EnriqueV]

I-5 Skylake/520 graphics/4gig RAM/UEFI boot/GPT

Any one had issues with supplemental updates and/or security updates booting very slowly after install and using approx. 750 more megs of memory? This has happened with recent updates to Catalina 10.15.1, Mojave security update 2019-001, and High Sierra security update 2019-006. I know that the first reboot after updates is usually slow but this problem with slow booting and hard drive thrashing persists after multiple reboots. It seems as though hard drive access is being channeled though a buffer. In one instance Catalina paused for a long time on reboot and a message appeared indicating that enough information had been found to re-enable the soft bloc. afterward Catalina booted normally but Mojave was booting so slow that it was practically unusable. After multiple reboots High sierra takes around a minute for the desktop to fully initialize after the login, but it was usable.

Does mac os use some kind of software input-output hard disk buffer that can be manually reset from the terminal? Disabling/enabling virtual memory paging seems to have no effect and the vm compressor mode is set to 2. The laptop only has 4 gig of memory but this has been enough to run all three os without boot issues in the past. Catalina on APFS, Mojave and High Sierra on H

FS+.

Any help appreciated.

[MaLd0n]

[ref]EnriqueV[/ref], all is fine here