On Sun, Jul 05, 2020 at 11:52:32AM -0400, Qian Cai wrote: > On Sun, Jul 05, 2020 at 08:58:54PM +0800, Feng Tang wrote: > > On Sun, Jul 05, 2020 at 08:15:03AM -0400, Qian Cai wrote: > > > > > > > > > > On Jul 5, 2020, at 12:45 AM, Feng Tang <feng.t...@intel.com> wrote: > > > > > > > > I did reproduce the problem, and from the debugging, this should > > > > be the same root cause as > > > > lore.kernel.org/lkml/20200526181459.gd...@lca.pw/ > > > > that loosing the batch cause some accuracy problem, and the solution of > > > > adding some sync is still needed, which is dicussed in > > > > > > Well, before taking any of those patches now to fix the regression, > > > we will need some performance data first. If it turned out the > > > original performance gain is no longer relevant anymore due to this > > > regression fix on top, it is best to drop this patchset and restore > > > that VM_WARN_ONCE, so you can retry later once you found a better > > > way to optimize. > > > > The fix of adding sync only happens when the memory policy is being > > changed to OVERCOMMIT_NEVER, which is not a frequent operation in > > normal cases. > > > > For the performance improvment data both in commit log and 0day report > > https://lore.kernel.org/lkml/20200622132548.GS5535@shao2-debian/ > > it is for the will-it-scale's mmap testcase, which will not runtime > > change memory overcommit policy, so the data should be still valid > > with this fix. > > Well, I would expect people are perfectly reasonable to use > OVERCOMMIT_NEVER for some workloads making it more frequent operations.
In my last email, I was not saying OVERCOMMIT_NEVER is not a normal case, but I don't think user will too frequently runtime change the overcommit policy. And the fix patch of syncing 'vm_committed_as' is only called when user calls 'sysctl -w vm.overcommit_memory=2'. > The question is now if any of those regression fixes would now regress > performance of OVERCOMMIT_NEVER workloads or just in-par with the data > before the patchset? For the original patchset, it keeps vm_committed_as unchanged for OVERCOMMIT_NEVER policy and enlarge it for the other 2 loose policies OVERCOMMIT_ALWAYS and OVERCOMMIT_GUESS, and I don't expect the "OVERCOMMIT_NEVER workloads" performance will be impacted. If you have suggetions for this kind of benchmarks, I can test them to better verify the patchset, thanks! - Feng > > Given now this patchset has had so much churn recently, I would think > "should be still valid" is not really the answer we are looking for. > > > > > Thanks, > > Feng > > > >
