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

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Date:   Thu, 2 Mar 2023 09:53:03 +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>,
        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 (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.

> 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