On Tue 20-11-18 11:35:12, Michal Hocko wrote: > Hi, > 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 [1] 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 [2] 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 [1] > and provide a consistent API to query the THP status both for each VMA > and process wide as well. Are there any other comments on these? I haven't heard any pushback so far so I will re-send with RFC dropped early next week. > > [1] http://lkml.kernel.org/r/http://lkml.kernel.org/r/alpine.DEB.2.21.1809241054050.224429@xxxxxxxxxxxxxxxxxxxxxxxxx > [2] http://lkml.kernel.org/r/20181002100531.GC4135@xxxxxxxxxxxxxx > -- Michal Hocko SUSE Labs
