linux-kernel - Re: [PATCH 0/2] Improve Zram by separating compression context from kswapd

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Message-ID: <CAKEwX=NfKrisQL-DBcNxBwK2ErK-u=MSzHNpETcuWWNBh9s9Bg@mail.gmail.com>
Date: Fri, 7 Mar 2025 15:03:34 -0800
From: Nhat Pham <nphamcs@...il.com>
To: Qun-Wei Lin <qun-wei.lin@...iatek.com>
Cc: Jens Axboe <axboe@...nel.dk>, Minchan Kim <minchan@...nel.org>, 
	Sergey Senozhatsky <senozhatsky@...omium.org>, Vishal Verma <vishal.l.verma@...el.com>, 
	Dan Williams <dan.j.williams@...el.com>, Dave Jiang <dave.jiang@...el.com>, 
	Ira Weiny <ira.weiny@...el.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, Chris Li <chrisl@...nel.org>, 
	Ryan Roberts <ryan.roberts@....com>, "Huang, Ying" <ying.huang@...el.com>, 
	Kairui Song <kasong@...cent.com>, Dan Schatzberg <schatzberg.dan@...il.com>, 
	Barry Song <baohua@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, 
	linux-kernel@...r.kernel.org, linux-block@...r.kernel.org, 
	nvdimm@...ts.linux.dev, linux-mm@...ck.org, 
	linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org, 
	Casper Li <casper.li@...iatek.com>, Chinwen Chang <chinwen.chang@...iatek.com>, 
	Andrew Yang <andrew.yang@...iatek.com>, James Hsu <james.hsu@...iatek.com>
Subject: Re: [PATCH 0/2] Improve Zram by separating compression context from kswapd

On Fri, Mar 7, 2025 at 4:02 AM Qun-Wei Lin <qun-wei.lin@...iatek.com> wrote:
>
> This patch series introduces a new mechanism called kcompressd to
> improve the efficiency of memory reclaiming in the operating system. The
> main goal is to separate the tasks of page scanning and page compression
> into distinct processes or threads, thereby reducing the load on the
> kswapd thread and enhancing overall system performance under high memory
> pressure conditions.

Please excuse my ignorance, but from your cover letter I still don't
quite get what is the problem here? And how would decouple compression
and scanning help?

>
> Problem:
>  In the current system, the kswapd thread is responsible for both
>  scanning the LRU pages and compressing pages into the ZRAM. This
>  combined responsibility can lead to significant performance bottlenecks,

What bottleneck are we talking about? Is one stage slower than the other?

>  especially under high memory pressure. The kswapd thread becomes a
>  single point of contention, causing delays in memory reclaiming and
>  overall system performance degradation.
>
> Target:
>  The target of this invention is to improve the efficiency of memory
>  reclaiming. By separating the tasks of page scanning and page
>  compression into distinct processes or threads, the system can handle
>  memory pressure more effectively.

I'm not a zram maintainer, so I'm definitely not trying to stop this
patch. But whatever problem zram is facing will likely occur with
zswap too, so I'd like to learn more :)