Hi Peng,
On Wed, Apr 24, 2024 at 12:29:25PM +0800, zhangpeng (AS) wrote:
> On 2024/4/18 22:20, Peng Zhang wrote:
>
> Any suggestions or opinions are welcome. Could someone please review
> this patch series?
> Thanks!
>
Sorry, I haven't been very active lately. This is what I remember
discussing a while back. I'll take a close look tomorrow.
Thanks,
Dennis
> > From: ZhangPeng <[email protected]>
> >
> > Since commit f1a7941243c1 ("mm: convert mm's rss stats into
> > percpu_counter"), the rss_stats have converted into percpu_counter,
> > which convert the error margin from (nr_threads * 64) to approximately
> > (nr_cpus ^ 2). However, the new percpu allocation in mm_init() causes a
> > performance regression on fork/exec/shell. Even after commit 14ef95be6f55
> > ("kernel/fork: group allocation/free of per-cpu counters for mm struct"),
> > the performance of fork/exec/shell is still poor compared to previous
> > kernel versions.
> >
> > To mitigate performance regression, we delay the allocation of percpu
> > memory for rss_stats. Therefore, we convert mm's rss stats to use
> > percpu_counter atomic mode. For single-thread processes, rss_stat is in
> > atomic mode, which reduces the memory consumption and performance
> > regression caused by using percpu. For multiple-thread processes,
> > rss_stat is switched to the percpu mode to reduce the error margin.
> > We convert rss_stats from atomic mode to percpu mode only when the
> > second thread is created.
> >
> > After lmbench test, we can get 2% ~ 4% performance improvement
> > for lmbench fork_proc/exec_proc/shell_proc and 6.7% performance
> > improvement for lmbench page_fault (before batch mode[1]).
> >
> > The test results are as follows:
> > base base+revert base+this patch
> >
> > fork_proc 416.3ms 400.0ms (3.9%) 398.6ms (4.2%)
> > exec_proc 2095.9ms 2061.1ms (1.7%) 2047.7ms (2.3%)
> > shell_proc 3028.2ms 2954.7ms (2.4%) 2961.2ms (2.2%)
> > page_fault 0.3603ms 0.3358ms (6.8%) 0.3361ms (6.7%)
> >
> > [1] https://lore.kernel.org/all/[email protected]/
> >
> > ChangeLog:
> > v2->v1:
> > - Convert rss_stats from atomic mode to percpu mode only when
> > the second thread is created per Jan Kara.
> > - Compared with v1, the performance data may be different due to
> > different test machines.
> >
> > ZhangPeng (2):
> > percpu_counter: introduce atomic mode for percpu_counter
> > mm: convert mm's rss stats to use atomic mode
> >
> > include/linux/mm.h | 50 +++++++++++++++++++++++++++++-----
> > include/linux/percpu_counter.h | 43 +++++++++++++++++++++++++++--
> > include/trace/events/kmem.h | 4 +--
> > kernel/fork.c | 18 +++++++-----
> > lib/percpu_counter.c | 31 +++++++++++++++++++--
> > 5 files changed, 125 insertions(+), 21 deletions(-)
> >
> --
> Best Regards,
> Peng
>