On Tue, 10 Jan 2017, Vlastimil Babka wrote: > > I get very confused by the /sys/kernel/mm/transparent_hugepage/defrag > > versus enabled flags, and this may be a terrible, even more confusing, > > idea: but I've been surprised and sad to see defrag with a "defer" > > option, but poor enabled without one; and it has crossed my mind that > > perhaps the peculiar "madvise+defer" syntax in defrag might rather be > > handled by "madvise" in defrag with "defer" in enabled? Or something > > like that: 4 x 4 possibilities instead of 5 x 3. > > But would all the possibilities make sense? For example, if I saw > "defer" in enabled, my first expectation would be that it would only use > khugepaged, and no THP page faults at all - possibly including madvised > regions. >
And this is why I've tried to minimize the config requirements and respect userspace decisions to do MADV_HUGEPAGE, MADV_NOHUGEPAGE, or set/clear PR_SET_THP_DISABLE because all these system-wide options combined with userspace syscalls truly seems unmaintainable and waay too confusing to correctly describe. Owell, I am fine with introducing yet-another-defrag-mode if it lets us move in a direction that supports our usecase.
