Re: [LKP] [lkp-robot] [mm] 9092c71bb7: blogbench.write_score -12.3% regression

Josef Bacik [off-list ref] writes:

On Thu, Aug 02, 2018 at 01:55:23PM +0800, Huang, Ying wrote:

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"Huang, Ying" [off-list ref] writes:

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Hi, Chris,

Chris Mason [off-list ref] writes:

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On 19 Jun 2018, at 23:51, Huang, Ying wrote:

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"Huang, Ying" [off-list ref] writes:

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Hi, Josef,

Do you have time to take a look at the regression?

kernel test robot [off-list ref] writes:

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Greeting,

FYI, we noticed a -12.3% regression of blogbench.write_score and
a +9.6% improvement
of blogbench.read_score due to commit:


commit: 9092c71bb724dba2ecba849eae69e5c9d39bd3d2 ("mm: use
sc->priority for slab shrink targets")
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git
master

in testcase: blogbench
on test machine: 16 threads Intel(R) Xeon(R) CPU D-1541 @
2.10GHz with 8G memory
with following parameters:

	disk: 1SSD
	fs: btrfs
	cpufreq_governor: performance

test-description: Blogbench is a portable filesystem benchmark
that tries to reproduce the load of a real-world busy file
server.
test-url:

I'm surprised, this patch is a big win in production here at FB.  I'll
have to reproduce these results to better understand what is going on.
My first guess is that since we have fewer inodes in slab, we're
reading more inodes from disk in order to do the writes.

But that should also make our read scores lower.

Any update on this?

Ping.

I can't reproduce this, and what's more it appears that blogbench doesn't use
much memory at all.  I have the slab shrinking tracepoints on and we never go
into this code at all, so I'm pretty sure these results are bogus.  How are you
running blogbench?  I'm doing blogbench -d /whatever, if I need to be doing
something else let me know.  But from what I can tell this thing uses less than
100m of memory, and on an 8gig of ram box we're never going to trip over this
code.  Thanks,

Thanks for looking at this.  In my testing, blogbench will eat up system
memory.  Please check the vmstat result attached.  The SSD disk size is
about 745GB.

Best Regards,
Huang, Ying