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From: Qian Cai <cai@lca.pw>
To: Feng Tang <feng.tang@intel.com>
Cc: kernel test robot <rong.a.chen@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@suse.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Matthew Wilcox <willy@infradead.org>,
	Mel Gorman <mgorman@suse.de>, Kees Cook <keescook@chromium.org>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Iurii Zaikin <yzaikin@google.com>,
	andi.kleen@intel.com, tim.c.chen@intel.com,
	dave.hansen@intel.com, ying.huang@intel.com, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, lkp@lists.01.org
Subject: Re: [mm] 4e2c82a409: ltp.overcommit_memory01.fail
Date: Sun, 5 Jul 2020 22:36:14 -0400
Message-ID: <20200706023614.GA1231@lca.pw> (raw)
In-Reply-To: <20200706014313.GB66252@shbuild999.sh.intel.com>

On Mon, Jul 06, 2020 at 09:43:13AM +0800, Feng Tang wrote:
> 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.tang@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.GD991@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!

Then, please capture those information into a proper commit log when you
submit the regression fix on top of the patchset, and CC PER-CPU MEMORY
ALLOCATOR maintainers, so they might be able to review it properly.

> 
> - 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
> > > 
> > > 

  reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-21  7:36 [PATCH v5 0/3] make vm_committed_as_batch aware of vm overcommit policy Feng Tang
2020-06-21  7:36 ` [PATCH v5 1/3] proc/meminfo: avoid open coded reading of vm_committed_as Feng Tang
2020-06-21  7:36 ` [PATCH v5 2/3] mm/util.c: make vm_memory_committed() more accurate Feng Tang
2020-06-21  7:36 ` [PATCH v5 3/3] mm: adjust vm_committed_as_batch according to vm overcommit policy Feng Tang
2020-06-22 13:25   ` [mm] 4e2c82a409: will-it-scale.per_process_ops 1894.6% improvement kernel test robot
     [not found]   ` <20200702063201.GG3874@shao2-debian>
2020-07-02  7:12     ` [mm] 4e2c82a409: ltp.overcommit_memory01.fail Feng Tang
2020-07-05  3:20       ` Qian Cai
2020-07-05  4:44       ` Feng Tang
2020-07-05 12:15         ` Qian Cai
2020-07-05 12:58           ` Feng Tang
2020-07-05 15:52             ` Qian Cai
2020-07-06  1:43               ` Feng Tang
2020-07-06  2:36                 ` Qian Cai [this message]
2020-07-06 13:24                   ` Feng Tang
2020-07-06 13:34                     ` Andi Kleen
2020-07-06 23:42                       ` Andrew Morton
2020-07-07  2:38                       ` Feng Tang
2020-07-07  4:00                         ` Huang, Ying
2020-07-07  5:41                           ` Feng Tang
2020-07-09  4:55                             ` Feng Tang
2020-07-09 13:40                               ` Qian Cai
2020-07-09 14:15                                 ` Feng Tang
2020-07-10  1:38                                   ` Feng Tang
2020-07-10  3:26                                     ` Qian Cai
2020-07-07  1:06                     ` Dennis Zhou
2020-07-07  3:24                       ` Feng Tang
2020-07-07 10:28               ` Michal Hocko
2020-06-24  9:45 ` [PATCH v5 0/3] make vm_committed_as_batch aware of vm overcommit policy Michal Hocko
2020-07-07 11:43 [mm] 4e2c82a409: ltp.overcommit_memory01.fail Qian Cai
2020-07-07 12:06 ` Michal Hocko
2020-07-07 13:04   ` Qian Cai
2020-07-07 13:56     ` Michal Hocko

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