On Tue 24-09-19 08:34:20, Linus Torvalds wrote: > On Tue, Sep 24, 2019 at 12:48 AM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > > The patch proposed by David is really non trivial wrt. potential side > > effects. > > The thing is, that's not an argument when we know that the current > state is garbage and has a lot of these non-trivial side effects that > are bad. > > So the patch by David _fixes_ a non-trivial bad side effect. > > You can't then say "there may be other non-trivial side effects that I > don't even know about" as an argument for saying it's bad. David at > least has numbers and an argument for his patch. All I am saying is that I am not able to wrap my head around this patch to provide a competent Ack. I also believe that the fix is targetting a wrong layer of the problem as explained in my review feedback. Appart from reclaim/compaction interaction mentioned by Vlastimil, it seems that it is an overly eager fallback to a remote node in the fast path that is causing a large part of the problem as well. Kcompactd is not eager enough to keep high order allocations ready for the fast path. This is not specific to THP we have many other high order allocations which are going to follow the same pattern, likely not visible in any counters but still having performance implications. Let's discuss technical details in the respective email thread -- Michal Hocko SUSE Labs
