linux-kernel - Re: [PATCHv2 3/6] zsmalloc: fine-grained inuse ratio based fullness grouping

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Date:   Wed, 1 Mar 2023 16:28:24 -0800
From:   Minchan Kim <minchan@...nel.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Yosry Ahmed <yosryahmed@...gle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv2 3/6] zsmalloc: fine-grained inuse ratio based fullness
 grouping

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
I thought we could handle zs_stats_size_show in the loop without
the specific each ratio definary.

Furthermore, above example, the special ZS_INUSE_RATIO_MAX will
be definary instead of hard coded 10.

    ZS_INUSE_RATIO_MAX = ZS_INUSE_RATIO_MIN + ZS_INUSER_RATIO_CLASS_SIZE

so, if we want to change the ratio later, we would need minimal
changes all the places instead of changing all the hard codeded
definary.