Re: [RFC PATCH v1 0/4] mm/damon: Introduce a huge page collapsing mechanism using auto tuning

[Gutierrez Asier]

On 5/1/2026 3:41 AM, SeongJae Park wrote:
> Hello Asier,
Hi, sorry for the delayed answer.
> 
> On Thu, 30 Apr 2026 13:41:35 +0000 <gutierrez.asier@xxxxxxxxxxxxxxxxxxx> wrote:
> 
>> From: Asier Gutierrez <gutierrez.asier@xxxxxxxxxxxxxxxxxxx>
>>
>> Overview
>> ================
> 
> Let's align the length of underline with the text.
> 
>>
>> This patch set introduces a new autotuning which allows to collapse
>> hot regions into hugepages.
>>
>> Motivation
>> ================
>>
>> Since TLB is a bottleneck for many systems, a way to optimize TLB
>> misses (or hits) is to use huge pages. Unfortunately, using "always"
>> in THP leads to memory fragmentation and memory waste. For this reason,
>> most application guides and system administrators suggest to disable THP.
> 
> I think the motivation should further explain why existing DAMOS features
> (access pattern-based targetting and quota auto-tuning with existing quota
> goals) are insufficient.  If that makes the text too long, I think the
> explanation for well-known THP benefit and problems can be reduced or skipped.
OK, I will elaborate it in further series.
> 
>>
>> Solution
>> ================
>>
>> A new autotuning quota goal[1], damos_get_used_hugepage_mem_bp, is
>> introduced, which checks the huge page consumption to total anonymous
>> memory consumption. This new quota mechanism reuses current autotuning
>> architecture.
> 
> The idea makes sense to me.
> 
> The name sounds bit redundant, though.  How about DAMOS_QUOTA_HUGEPAGE_BP for
> the enum, and hugeapge_bp for sysfs input?
Agree. In fact, DAMOS_QUOTA_HUGEPAGE_BP would make sense to keep it
consistent with the quota naming.
> 
>>
>> A new module is introduced to demonstrate the use of huge pages
>> collapse autotuning. The module launches a kdamond thread for a 
>> certain task provided by the user through monitored_pid module argument.
> 
> If it is only for demonstration, I think it is more fit to be a sample module
> (placed under samples/damon/).
We are testing this in a bare metal MySQL server. Maybe the description
was not the most accurate.
>>
>> This module also has a user autotuning knob which allows the user to
>> adjust the aggressiveness of page collapsing.
>>
>> Benchmarks
>> ================
>> In progress, will add them in the next RFC series.
> 
> Looking forward to!
> 
> I may request not that much test results for the quota goal.  If the module is
> not just a sample but for a real world use case, I may hope somewhat reasonable
> test resulsts.
OK, will do it.
>>
>> TODO
>> ================
>>
>> - Since DAMOS_COLLAPSE is not in upstream and this is just a
>>   RFC, I have used DAMOS_HUGEPAGE instead. This will change
>>   to DAMOS_COLLAPSE in future series.
> 
> It is now in mm-new and it is recommended to use it as a baseline for DAMON
> patches.  So please feel free to use DAMOS_COLLAPSE from the next version,
> unless there is a reason to worry if DAMOS_COLLAPSE will be dropped from
> mm-new.
Thanks.
>>
>> Patches Sequence
>> ================
>> Patch 1 -> damon_modules_new_vaddr_ctx_target
>> Patch 2 -> Introduce DAMOS_QUOTA_HUGEPAGE and autotuning
>> Patch 3 -> Module that demonstrates how to use DAMOS_QUOTA_HUGEPAGE
>>            and the new VADDR ctx creation
>> Patch 4 -> Documentation
>>
>> [1] https://lore.kernel.org/e67f05ad-dbb9-45e6-ba30-b167a99ac67d@xxxxxxxxxxxxxxxxxxx
> 
> Adding more context about what this link is would be nice.  I can find the link
> marker from the above text, but I was unable to expect what this is without
> opening the link.
> 
> 
> Thanks,
> SJ
> 
> [...]
> 

-- 
Asier Gutierrez
Huawei