Sender: Minchan Kim <minchan.kim@gmail.com>
Date:   Thu, 2 Mar 2023 16:20:43 -0800
From:   Minchan Kim <minchan@kernel.org>
To:     Sergey Senozhatsky <senozhatsky@chromium.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Yosry Ahmed <yosryahmed@google.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCHv2 3/6] zsmalloc: fine-grained inuse ratio based fullness
 grouping
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On Thu, Mar 02, 2023 at 09:53:03AM +0900, Sergey Senozhatsky wrote:
> On (23/03/01 16:28), Minchan Kim wrote:
> > On Wed, Mar 01, 2023 at 05:55:44PM +0900, Sergey Senozhatsky wrote:
> > > On (23/02/28 14:53), Minchan Kim wrote:
> > > > BTW, I still prefer the enum instead of 10 define.
> > > > 
> > > > enum fullness_group {
> > > >     ZS_EMPTY,
> > > >     ZS_INUSE_RATIO_MIN,
> > > >     ZS_INUSE_RATIO_ALMOST_FULL = 7,
> > > >     ZS_INUSE_RATIO_MAX = 10,
> > > >     ZS_FULL,
> > > >     NR_ZS_FULLNESS,
> > > > }
> > > 
> > > For educational purposes, may I ask what do enums give us? We
> > > always use integers - int:4 in zspage fullness, int for arrays
> > > offsets and we cast to plain integers in get/set stats. So those
> > > enums exist only at declaration point, and plain int otherwise.
> > > What are the benefits over #defines?
> > 
> > Well, I just didn't like the 12 hard coded define *list* values
> > and never used other places except zs_stats_size_show since
> 
> If we have two enums, then we need more lines
> 
> enum fullness {
> 	ZS_INUSE_RATIO_0
> 	...
> 	ZS_INUSE_RATIO_100
> }
> 
> enum stats {
> 	INUSE_RATIO_0
> 	...
> 	INUSE_RATIO_100
> 
> 	// the rest of stats
> }
> 
> and then we use int:4 fullness value to access stats.

Yeah. I don't see any problem unless I miss your point.

> 
> > I thought we could handle zs_stats_size_show in the loop without
> > the specific each ratio definary.
> 
> For per inuse ratio zs_stats_size_show() we need to access stats
> individually:
> 
> 	inuse10, inuse20, inuse30, ... inuse99

Does it need specific index in the enum list?

I don't mind having all the hard coded index if it's *necessary*
but wanted to try we could make the index with base + index
on demand in the loop via simple arithmetic.