On Tue 27-11-18 19:17:27, Michal Hocko wrote: > On Tue 27-11-18 09:08:50, Linus Torvalds wrote: > > On Mon, Nov 26, 2018 at 10:24 PM kernel test robot > > <rong.a.c...@intel.com> wrote: > > > > > > FYI, we noticed a -61.3% regression of vm-scalability.throughput due > > > to commit ac5b2c18911f ("mm: thp: relax __GFP_THISNODE for > > > MADV_HUGEPAGE mappings") > > > > Well, that's certainly noticeable and not good. > > > > Andrea, I suspect it might be causing fights with auto numa migration.. > > > > Lots more system time, but also look at this: > > > > > 1122389 ± 9% +17.2% 1315380 ± 4% proc-vmstat.numa_hit > > > 214722 ± 5% +21.6% 261076 ± 3% > > > proc-vmstat.numa_huge_pte_updates > > > 1108142 ± 9% +17.4% 1300857 ± 4% proc-vmstat.numa_local > > > 145368 ± 48% +63.1% 237050 ± 17% proc-vmstat.numa_miss > > > 159615 ± 44% +57.6% 251573 ± 16% proc-vmstat.numa_other > > > 185.50 ± 81% +8278.6% 15542 ± 40% > > > proc-vmstat.numa_pages_migrated > > > > Should the commit be reverted? Or perhaps at least modified? > > Well, the commit is trying to revert to the behavior before > 5265047ac301 because there are real usecases that suffered from that > change and bug reports as a result of that. > > will-it-scale is certainly worth considering but it is an artificial > testcase. A higher NUMA miss rate is an expected side effect of the > patch because the fallback to a different NUMA node is more likely. The > __GFP_THISNODE side effect is basically introducing node-reclaim > behavior for THPages. Another thing is that there is no good behavior > for everybody. Reclaim locally vs. THP on a remote node is hard to > tell by default. We have discussed that at length and there were some > conclusions. One of them is that we need a numa policy to tell whether > a expensive localility is preferred over remote allocation. Also we > definitely need a better pro-active defragmentation to allow larger > pages on a local node. This is a work in progress and this patch is a > stop gap fix.
Btw. the associated discussion is http://lkml.kernel.org/r/20180925120326.24392-1-mho...@kernel.org -- Michal Hocko SUSE Labs