In 1997, Dillon gained commit access to the FreeBSD code and heavily contributed to the virtual memory subsystem,[10] amongst other contributions.
Concerned with problems he saw in the direction FreeBSD 5.x was headed in regards to concurrency,[10] and coupled with the fact that Dillon's access to the FreeBSD source code repository was revoked due to a falling-out with other FreeBSD developers, he started the DragonFly BSD project in 2003, implementing the SMP model using light-weight kernel threads.[3][11] The DragonFly project also led to the development of a new userspace kernel virtualisation technique in 2006, called Virtual Kernel,[3][12] originally to ease the development and testing of subsequent kernel-level features;[13] a new file system, called HAMMER, which he created using B-trees; HAMMER was declared production-ready with DragonFly 2.2 in 2009;[12] and, subsequently, HAMMER2, declared stable in 2018 with DragonFly 5.2.
Most recently, Dillon has gotten a number of headlines around CPUerrata. In 2007, this was after Theo de Raadt of OpenBSD raised the alarm around the seriousness of some of the errata for Intel Core 2 family of CPUs.[14] Dillon has independently evaluated Intel's errata, and did an overview of Intel Core errata as well, suggesting that several of them were so serious as to warrant avoiding any processor where the issues remain unfixed.[14] Dillon has since been a fan of AMD processors, and, subsequently in 2012, he has discovered a brand-new deficiency in some AMD processors for which no existing erratum existed at the time.[15] Dillon continued his work around CPU issues as late as 2018, presenting solutions to tackle the latest security vulnerabilities like Meltdown, some of which have been subsequently adopted by OpenBSD as well.[16]
Dillon was a frequent guest on bsdtalk during the runtime of the show,[17] and was interviewed several times for KernelTrap.[5][6]
^David Chisnall (2012). "Why Go?". The Go Programming Language Phrasebook (1st ed.). Addison-Wesley Professional. p. 5. ISBN978-0-321-81714-3. In creating DragonFly BSD, Matt Dillon observed that there was no point in creating an N:M threading model—where N userspace threads are multiplexed on top of M kernel threads—because C code that uses more than a handful of threads is very rare.
^"OpenBSD releases Meltdown patch". The Register. 2018-02-23. Retrieved 2019-03-02. Part of the OpenBSD solution used the approach employed by Matthew Dillon in his DragonFly BSD – the per-CPU page layout aspect.