linux-kernel - Re: [RFC PATCH 0/5] Memory access profiler(IBS) driven NUMA balancing

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Date:   Mon, 6 Mar 2023 21:00:47 +0530
From:   Bharata B Rao <bharata@....com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, mgorman@...e.de,
        peterz@...radead.org, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org,
        akpm@...ux-foundation.org, luto@...nel.org, tglx@...utronix.de,
        yue.li@...verge.com, Ravikumar.Bangoria@....com
Subject: Re: [RFC PATCH 0/5] Memory access profiler(IBS) driven NUMA balancing

On 03-Mar-23 11:23 AM, Huang, Ying wrote:
> 
> What is the memory accessing pattern of the workload?  Uniform random or
> something like Gauss distribution?

Multiple iterations of uniform access from beginning to end of the
memory region.

> 
> Anyway, it may take some time for the original method to scan enough
> memory space to trigger enough hint page fault.  We can check
> numa_pte_updates to check whether enough virtual space has been scanned.

I see that numa_hint_faults is way higher (sometimes close to 5 times)
than numa_pte_updates. This doesn't make sense. Very rarely I do see
saner numbers and when that happens the benchmark score is also much better.

Looks like an issue with the default kernel itself. I will debug this
further and get back.

Regards,
Bharata.