Hi, I've posted this as an RFC [1] and there didn't seem to be any pushback so I am posting it for inclusion. If there are any concerns, please speak up. Original cover: This series of three patches aims at making THP eligibility reporting much more robust and long term sustainable. The trigger for the change is a regression report [2] and the long follow up discussion. In short the specific application didn't have good API to query whether a particular mapping can be backed by THP so it has used VMA flags to workaround that. These flags represent a deep internal state of VMAs and as such they should be used by userspace with a great deal of caution. A similar has happened for [3] when users complained that VM_MIXEDMAP is no longer set on DAX mappings. Again a lack of a proper API led to an abuse. The first patch in the series tries to emphasise that that the semantic of flags might change and any application consuming those should be really careful. The remaining two patches provide a more suitable interface to address [2] and provide a consistent API to query the THP status both for each VMA and process wide as well. [1] http://lkml.kernel.org/r/20181120103515.25280-1-mhocko@xxxxxxxxxx [2] http://lkml.kernel.org/r/http://lkml.kernel.org/r/alpine.DEB.2.21.1809241054050.224429@xxxxxxxxxxxxxxxxxxxxxxxxx [3] http://lkml.kernel.org/r/20181002100531.GC4135@xxxxxxxxxxxxxx
