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

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Message-ID: <20230303010643.GA4022757@google.com>
Date:   Fri, 3 Mar 2023 10:06:43 +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 (23/03/02 16:20), Minchan Kim wrote:
> 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.

OK. How about having one enum? E.g. "zs_flags" or something which
will contain all our constants?

Otherwise I can create two big enums for fullness and stats.
What's your preference on inuse_0 and inuse_100 naming? Do we
keep unified naming or should it be INUSE_MIN/INUSE_MAX or
EMPTY/FULL?

> > 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?

If we report per inuse group then yes:

	sprintf("... %lu %lu ..... %lu %lu ...\n",
		...
		get_stat(ZS_INUSE_RATIO_10),
		get_stat(ZS_INUSE_RATIO_20),
		get_stat(ZS_INUSE_RATIO_30),
		...
		get_stat(ZS_INUSE_RATIO_99),
		...);