FWIW, Debian 9 (stretch) has it set to "madvise", but my Debian unstable machine has it to "always". Looking further, I can see that /boot/config-4.12.0-1-amd64

FWIW, Debian 9 (stretch) has it set to "madvise", but my Debian unstable machine has it to "always". Looking further, I can see that /boot/config-4.12.0-1-amd64 has: # CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS is not set CONFIG_TRANSPARENT_HUGEPAGE_MADVISE=y and /boot/config-4.13.0-1-amd64 has: CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y # CONFIG_TRANSPARENT_HUGEPAGE_MADVISE is not set So this is a recent change. Edit: The linux kernel source says the default is always (in mm/Kconfig), and that's been true since 2011. The debian package changelog says the change occurred in 4.13.4-1: * thp: Enable TRANSPARENT_HUGEPAGE_ALWAYS instead of TRANSPARENT_HUGEPAGE_MADVISE The reason is not given in the changelog itself, but it's given in the git log of the debian packaging: As advised by Andrea Arcangeli - since commit 444eb2a449ef "mm: thp: set THP defrag by default to madvise and add a stall-free defrag option" this will generally be best for performance. https://anonscm.debian.org/cgit/kernel/linux.git/commit/debian/changelog?id=611a8e67260e8b8190ab991206a3867681d6df91 https://anonscm.debian.org/cgit/kernel/linux.git/commit/debi... Edit 2: The mentioned commit (444eb2a449ef) dates back to 4.6, so presumably, at least some performance issues with transparent huge pages may be gone since that version of the kernel.