linux-kernel - Re: [PATCH v22 00/18] Introduce Data Access MONitor (DAMON)

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Date:   Wed, 11 Nov 2020 17:41:13 +0100
From:   SeongJae Park <sjpark@...zon.com>
To:     SeongJae Park <sjpark@...zon.com>
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Subject: Re: [PATCH v22 00/18] Introduce Data Access MONitor (DAMON)

Hi, I'd like to remind you that I'm still waiting more reviews.  Any comments
are welcome.


Thanks,
SeongJae Park

On Tue, 20 Oct 2020 10:59:22 +0200 SeongJae Park <sjpark@...zon.com> wrote:

> From: SeongJae Park <sjpark@...zon.de>
> 
> Changes from Previous Version (v21)
> ===================================
> 
> This version contains below minor changes.
> 
> - Fix build warnings and errors (kernel test robot)
> - Fix a memory leak (kmemleak)
> - Respect KUNIT_ALL_TESTS
> - Rebase on v5.9
> - Update the evaluation results
> 
> Introduction
> ============
> 
> DAMON is a data access monitoring framework for the Linux kernel.  The core
> mechanisms of DAMON called 'region based sampling' and 'adaptive regions
> adjustment' (refer to 'mechanisms.rst' in the 11th patch of this patchset for
> the detail) make it
> 
>  - accurate (The monitored information is useful for DRAM level memory
>    management. It might not appropriate for Cache-level accuracy, though.),
>  - light-weight (The monitoring overhead is low enough to be applied online
>    while making no impact on the performance of the target workloads.), and
>  - scalable (the upper-bound of the instrumentation overhead is controllable
>    regardless of the size of target workloads.).
> 
> Using this framework, therefore, several memory management mechanisms such as
> reclamation and THP can be optimized to aware real data access patterns.
> Experimental access pattern aware memory management optimization works that
> incurring high instrumentation overhead will be able to have another try.
> 
> Though DAMON is for kernel subsystems, it can be easily exposed to the user
> space by writing a DAMON-wrapper kernel subsystem.  Then, user space users who
> have some special workloads will be able to write personalized tools or
> applications for deeper understanding and specialized optimizations of their
> systems.
> 
> Evaluations
> ===========
> 
> We evaluated DAMON's overhead, monitoring quality and usefulness using 24
> realistic workloads on my QEMU/KVM based virtual machine running a kernel that
> v22 DAMON patchset is applied.
> 
> DAMON is lightweight.  It increases system memory usage by 0.25% and slows
> target workloads down by 0.89%.
> 
> DAMON is accurate and useful for memory management optimizations.  An
> experimental DAMON-based operation scheme for THP, 'ethp', removes 81.73% of
> THP memory overheads while preserving 95.29% of THP speedup.  Another
> experimental DAMON-based 'proactive reclamation' implementation, 'prcl',
> reduces 91.30% of residential sets and 23.45% of system memory footprint while
> incurring only 2.08% runtime overhead in the best case (parsec3/freqmine).
> 
> NOTE that the experimentail THP optimization and proactive reclamation are not
> for production but only for proof of concepts.
> 
> Please refer to the official document[1] or "Documentation/admin-guide/mm: Add
> a document for DAMON" patch in this patchset for detailed evaluation setup and
> results.
> 
> [1] https://damonitor.github.io/doc/html/latest-damon/admin-guide/mm/damon/eval.html
>