linux-kernel - Re: [PATCH 2/2] kcompressd: Add Kcompressd for accelerated zram compression

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Message-ID: <mzythwqmi22gmuunmqcyyn7eiggevvrzkpqmjkoxsj4q4jc46s@64jdco5s6spa>
Date: Tue, 11 Mar 2025 14:02:42 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Nhat Pham <nphamcs@...il.com>
Cc: Barry Song <21cnbao@...il.com>, Qun-Wei Lin <qun-wei.lin@...iatek.com>, 
	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>, 
	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 2/2] kcompressd: Add Kcompressd for accelerated zram
 compression

On (25/03/07 15:13), Nhat Pham wrote:
> > > +config KCOMPRESSD
> > > +       tristate "Kcompressd: Accelerated zram compression"
> > > +       depends on ZRAM
> > > +       help
> > > +         Kcompressd creates multiple daemons to accelerate the compression of pages
> > > +         in zram, offloading this time-consuming task from the zram driver.
> > > +
> > > +         This approach improves system efficiency by handling page compression separately,
> > > +         which was originally done by kswapd or direct reclaim.
> >
> > For direct reclaim, we were previously able to compress using multiple CPUs
> > with multi-threading.
> > After your patch, it seems that only a single thread/CPU is used for compression
> > so it won't necessarily improve direct reclaim performance?
> >
> > Even for kswapd, we used to have multiple threads like [kswapd0], [kswapd1],
> > and [kswapd2] for different nodes. Now, are we also limited to just one thread?
> > I also wonder if this could be handled at the vmscan level instead of the zram
> > level. then it might potentially help other sync devices or even zswap later.
> 
> Agree. A shared solution would be much appreciated. We can keep the
> kcompressd idea, but have it accept IO work from multiple sources
> (zram, zswap, whatever) through a shared API.

I guess it also need to take swapoff into consideration (especially
if it takes I/O from multiple sources)?