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

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Message-ID: <Z9HOavSkFf01K9xh@google.com>
Date: Wed, 12 Mar 2025 11:11:54 -0700
From: Minchan Kim <minchan@...nel.org>
To: Qun-Wei Lin <qun-wei.lin@...iatek.com>
Cc: Jens Axboe <axboe@...nel.dk>,
	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

Hi Qun-Wei

On Fri, Mar 07, 2025 at 08:01:02PM +0800, Qun-Wei Lin 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.
> 
> 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,
>  especially under high memory pressure. The kswapd thread becomes a
>  single point of contention, causing delays in memory reclaiming and
>  overall system performance degradation.

Isn't it general problem if backend for swap is slow(but synchronous)?
I think zram need to support asynchrnous IO(can do introduce multiple
threads to compress batched pages) and doesn't declare it's
synchrnous device for the case.