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    SubjectRe: [mm] 8cc621d2f4: fio.write_iops -21.8% regression
    On Mon, May 24, 2021 at 10:37:49AM -0700, Chris Goldsworthy wrote:
    > Hi Minchan,
    >
    > This looks good to me, I just have some minor feedback.
    >
    > Thanks,

    Hi Chris,

    Thanks for the review. Please see below.

    >
    > Chris.
    >
    > On 2021-05-20 11:36, Minchan Kim wrote:
    > > On Thu, May 20, 2021 at 04:31:44PM +0800, kernel test robot wrote:
    > > >
    > > >
    > > > Greeting,
    > > >
    > > > FYI, we noticed a -21.8% regression of fio.write_iops due to commit:
    > > >
    > > >
    > > > commit: 8cc621d2f45ddd3dc664024a647ee7adf48d79a5 ("mm: fs:
    > > > invalidate BH LRU during page migration")
    > > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
    > > >
    > > >
    > > > in testcase: fio-basic
    > > > on test machine: 96 threads 2 sockets Intel(R) Xeon(R) Gold 6252 CPU
    > > > @ 2.10GHz with 256G memory
    > > > with following parameters:
    > > >
    > > > disk: 2pmem
    > > > fs: ext4
    > > > runtime: 200s
    > > > nr_task: 50%
    > > > time_based: tb
    > > > rw: randwrite
    > > > bs: 4k
    > > > ioengine: libaio
    > > > test_size: 200G
    > > > cpufreq_governor: performance
    > > > ucode: 0x5003006
    > > >
    > > > test-description: Fio is a tool that will spawn a number of threads
    > > > or processes doing a particular type of I/O action as specified by
    > > > the user.
    > > > test-url: https://github.com/axboe/fio
    > > >
    > > >
    > > >
    > > > If you fix the issue, kindly add following tag
    > > > Reported-by: kernel test robot <oliver.sang@intel.com>
    > > >
    > > >
    > > > Details are as below:
    > > > -------------------------------------------------------------------------------------------------->
    > > >
    > > >
    > > > To reproduce:
    > > >
    > > > git clone https://github.com/intel/lkp-tests.git
    > > > cd lkp-tests
    > > > bin/lkp install job.yaml # job file is
    > > > attached in this email
    > > > bin/lkp split-job --compatible job.yaml # generate the yaml
    > > > file for lkp run
    > > > bin/lkp run generated-yaml-file
    > >
    > > Hi,
    > >
    > > I tried to insall the lkp-test in my machine by following above guide
    > > but failed
    > > due to package problems(I guess it's my problem since I use something
    > > particular
    > > environement). However, I guess it comes from increased miss ratio of
    > > bh_lrus
    > > since the patch caused more frequent invalidation of the bh_lrus calls
    > > compared
    > > to old. For example, lru_add_drain could be called from several hot
    > > places(e.g.,
    > > unmap and pagevec_release from several path) and it could keeps
    > > invalidating
    > > bh_lrus.
    > >
    > > IMO, we should move the overhead from such hot path to cold one. How
    > > about this?
    > >
    > > From ebf4ede1cf32fb14d85f0015a3693cb8e1b8dbfe Mon Sep 17 00:00:00 2001
    > > From: Minchan Kim <minchan@kernel.org>
    > > Date: Thu, 20 May 2021 11:17:56 -0700
    > > Subject: [PATCH] invalidate bh_lrus only at lru_add_drain_all
    > >
    > > Not-Yet-Signed-off-by: Minchan Kim <minchan@kernel.org>
    > > ---
    > > mm/swap.c | 15 +++++++++++++--
    > > 1 file changed, 13 insertions(+), 2 deletions(-)
    > >
    > > diff --git a/mm/swap.c b/mm/swap.c
    > > index dfb48cf9c2c9..d6168449e28c 100644
    > > --- a/mm/swap.c
    > > +++ b/mm/swap.c
    > > @@ -642,7 +642,6 @@ void lru_add_drain_cpu(int cpu)
    > > pagevec_lru_move_fn(pvec, lru_lazyfree_fn);
    > >
    > > activate_page_drain(cpu);
    > > - invalidate_bh_lrus_cpu(cpu);
    > > }
    > >
    > > /**
    > > @@ -725,6 +724,17 @@ void lru_add_drain(void)
    > > local_unlock(&lru_pvecs.lock);
    > > }
    > >
    > > +void lru_and_bh_lrus_drain(void)
    > > +{
    > > + int cpu;
    > > +
    > > + local_lock(&lru_pvecs.lock);
    > > + cpu = smp_processor_id();
    > > + lru_add_drain_cpu(cpu);
    > > + local_unlock(&lru_pvecs.lock);
    > > + invalidate_bh_lrus_cpu(cpu);
    > > +}
    > > +
    >
    > Nit: drop int cpu?

    Do you mean to suggest using smp_processor_id at both places
    instead of local varaible? Since the invalidate_bh_lrus_cpu
    is called out of the lru_pvecs.lock, I wanted to express
    the draining happens at the same CPU via storing the CPU.

    >
    > > void lru_add_drain_cpu_zone(struct zone *zone)
    > > {
    > > local_lock(&lru_pvecs.lock);
    > > @@ -739,7 +749,7 @@ static DEFINE_PER_CPU(struct work_struct,
    > > lru_add_drain_work);
    > >
    > > static void lru_add_drain_per_cpu(struct work_struct *dummy)
    > > {
    > > - lru_add_drain();
    > > + lru_and_bh_lrus_drain();
    > > }
    > >
    > > /*
    > > @@ -881,6 +891,7 @@ void lru_cache_disable(void)
    > > __lru_add_drain_all(true);
    > > #else
    > > lru_add_drain();
    > > + invalidate_bh_lrus_cpu(smp_processor_id());
    > > #endif
    > > }
    >
    > Can't we replace the call to lru_add_drain() and
    > invalidate_bh_lrus_cpu(smp_processor_id()) with a single call to
    > lru_and_bh_lrus_drain()?

    Good idea.

    Thanks!

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