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

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Date:   Sat, 5 Nov 2022 08:41:37 +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 (22/11/04 10:43), Minchan Kim wrote:
> > > 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.
> > 
> > Or pass priority= so that interface that uses algorithms has the
> > same keyword that the interface that configures those algorithms.
> 
> Hmm, why do we need algo_idx here if we already set up every
> fields at algorithm setup time?
> 
> My understaind(assuming default(i.e., primary) algo is lzo) is
> 
>     echo "name=lz4 priority=1" > recomp_algo
>     echo "name=lz5 priority=2" > recomp_algo
> 
>     echo "type=huge threshold=3000" > recompress
> 
> It will try compress every objects which greater than 3000B with lz4 first
> and then lz5 if it's stillgreater or equal than 3000(or same size class).

One can be SW one can be HW. So I thought about having flexibility here.
Instead of doing

	for (idx = 1; idx < MAX_IDX; idx++) {
		len = zcomp_compress(zram->comps[idx]);
		if (len <= threshold)
			break;
	}

We would just directly use the suggested algo.

But we probably don't need that param at all and can use
the loop instead?

[..]
>     echo "name=lz4 priority=1" > recomp_algo
>     echo "name=lz5 priority=2" > recomp_algo
>
>     # or I realized to change lz5 to lz7 so
>     echo "name=lz6 priority=2" > recomp_algo

So the latter should delete lz5 at idx 2 and put lz6 there?
I can add that.