linux-kernel - Re: [PATCHv4 2/9] zram: Add recompression algorithm sysfs knob

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Date:   Fri, 4 Nov 2022 12:18:43 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nitin Gupta <ngupta@...are.org>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCHv4 2/9] zram: Add recompression algorithm sysfs knob

On (22/11/03 09:34), Minchan Kim wrote:
> > > My point is that we don't need to implement it atm but makes the
> > > interface to open the possibility for future extension.
> > > 
> > > What do you think?
> > 
> > So, as far as I understand, we don't have reason to add remove_recomp_algo
> > right now. And existing recomp_algo does not enforce any particular format,
> > it can be extended. Right now we accept "$name" but can do something like
> > "$name:$priority". The only thing that we probably need to do is rename
> > recomp_algo to either add_recomp_algo or register_recomp_algo?
> 
> Yeah, I like the name and priority format.
> 
> Only question is how we could support algorithm selection change
> under considering multiple secondary algorithms.

So what I was thinking about, and I'm still in the mental model that
re-compression is a user-space event, just like writeback, extension
of recompress sysfs knob with "algo_index" (or something similar) which
will mirror algorithm priority.

Example:

Configure 2 alternative algos, with priority 1 and 2

	echo "name=lz4 priority=1" > recomp_algo
	echo "name=lz5 priority=2" > recomp_algo

Recompress pages using algo 1 and algo 2

	echo "type=huge threshold=3000 algo_idx=1" > recompress
	echo "type=idle threshold=2000 algo_idx=2" > recompress

Maybe we can even pass algo name instead of idx.