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

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Date:   Fri, 4 Nov 2022 09:34:07 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     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 Fri, Nov 04, 2022 at 12:18:43PM +0900, Sergey Senozhatsky wrote:
> 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.

Let's use name rather than index.