Re: [LKP] Re: [mm] 8cc621d2f4: fio.write_iops -21.8% regression

Minchan Kim
2021-09-07T16:56:01Z

Hi,

On Fri, Sep 03, 2021 at 03:11:33PM +0800, Xing, Zhengjun wrote:
> Hi Minchan,
>
>     Do you have time to look at this? I re-test it in  v5.14, the regression
> still existed. Thanks.

Reminding me the issue, again, Xing. That's because the patch
was not merged yet so let me send it again.

Andrew?

From 8caadeb49d82403a08643dfbdb0b7749017c00bb Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Tue, 25 May 2021 08:19:17 -0700
Subject: [PATCH] mm: fs: invalidate bh_lrus for only cold path

kernel test robot reported the regression of fio.write_iops[1]
with [2].

Since lru_add_drain is called frequently, invalidate bh_lrus
there could increase bh_lrus cache miss ratio, which needs
more IO in the end.

This patch moves the bh_lrus invalidation from the hot path(
e.g., zap_page_range, pagevec_release) to cold path(i.e.,
lru_add_drain_all, lru_cache_disable).

[1] https://lore.kernel.org/lkml/20210520083144.GD14190@xsang-OptiPlex-9020/
[2] 8cc621d2f45d, mm: fs: invalidate BH LRU during page migration
Cc: Xing, Zhengjun <zhengjun.xing@intel.com>
Reviewed-by: Chris Goldsworthy <cgoldswo@codeaurora.org>
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
mm/swap.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index 1958d5feb148..3e25d99a9dbb 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);
}

+static void lru_add_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);
+}
+
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_add_and_bh_lrus_drain();
}

/*
@@ -880,7 +890,7 @@ void lru_cache_disable(void)
*/
__lru_add_drain_all(true);
#else
- lru_add_drain();
+ lru_add_and_bh_lrus_drain();
#endif
}

--
2.31.1.818.g46aad6cb9e-goog