linux-kernel - Re: [PATCH v3 0/4] mm/folio_zero

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Message-ID: <b7423090-4504-4d68-878f-7ea4cde2af45@amd.com>
Date: Wed, 23 Apr 2025 13:42:58 +0530
From: Raghavendra K T <raghavendra.kt@....com>
To: Ankur Arora <ankur.a.arora@...cle.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
 torvalds@...ux-foundation.org, akpm@...ux-foundation.org, bp@...en8.de,
 dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
 luto@...nel.org, peterz@...radead.org, paulmck@...nel.org,
 rostedt@...dmis.org, tglx@...utronix.de, willy@...radead.org,
 jon.grimm@....com, bharata@....com, boris.ostrovsky@...cle.com,
 konrad.wilk@...cle.com
Subject: Re: [PATCH v3 0/4] mm/folio_zero_user: add multi-page clearing



On 4/23/2025 12:52 AM, Ankur Arora wrote:
> 
> Raghavendra K T <raghavendra.kt@....com> writes:
[...]
>>
>> SUT: AMD EPYC 9B24 (Genoa) preempt=lazy
>>
>> metric = time taken in sec (lower is better). total SIZE=64GB
>>                   mm/folio_zero_user    x86/folio_zero_user     change
>>    pg-sz=1GB       2.47044  +-  0.38%    1.060877  +-  0.07%    57.06
>>    pg-sz=2MB       5.098403 +-  0.01%    2.52015   +-  0.36%    50.57
> 
> 
> Just to translate it into the same units I was using above:
> 
>                    mm/folio_zero_user        x86/folio_zero_user
>     pg-sz=1GB       25.91 GBps +-  0.38%    60.37 GBps +-  0.07%
>     pg-sz=2MB       12.57 GBps +-  0.01%    25.39 GBps +-  0.36%
> 
> That's a decent improvement over Milan. Btw, are you using boost=1?
> 

yes boost=1

> Also, any idea why the huge delta in the mm/folio_zero_user 2MB, 1GB
> cases? Both of these are doing 4k page at a time, so the huge delta
> is a little head scratching.
> 
> There's a gap on Milan as well but it is much smaller.
> 

Need to think/analyze further, but from perf stat I see
glaring difference in:
			2M		1G
pagefaults		32,906		202
iTLB-load-misses	44,490		156

- Raghu