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

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Message-ID: <Y//qIR8tTZjVCFgD@google.com>
Date:   Wed, 1 Mar 2023 16:13:21 -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 01:05:20PM +0900, Sergey Senozhatsky wrote:
> On (23/02/28 14:53), Minchan Kim wrote:
> [..]
> > > As of why I decided to go with defines, this is because zspage fullness
> > > values and class stats are two conceptually different things, they don't
> > > really fit in one single enum, unless enum's name is "zs_constants".
> > > What do you think?
> > 
> > Agree. We don't need to combine them, then. 
> > 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,
> > }
> 
> So we keep enum nesting? Sorry, I'm not exactly following.

Sorry, I meant let's keep separating them since they are different
things conceptually as you mentioned.

> 
> We have fullness values (which we use independently) and stats array
> which has overlapping offsets with fullness values.
> 
> [..]
> > > I can change it to
> > > 
> > > 	for (r = ZS_INUSE_RATIO_10; r <= ZS_INUSE_RATIO_70; r++)
> > > and
> > > 	for (r = ZS_INUSE_RATIO_80; r <= ZS_INUSE_RATIO_99; r++)
> > > 
> > > which would be safer than using hard-coded numbers.
> > 
> > I didn't mean to have hard code either but just wanted to show
> > the intention to use the loop.
> 
> Got it. I just wanted to show that being very verbose (having every
> constant documented) is nice :)
> 
> > > 
> > > Shall we actually instead report per inuse ratio stats instead? I sort
> > > of don't see too many reasons to keep that below/above 3/4 thing.
> > 
> > Oh, yeah. Since it's debugfs, we would get excuse to break.
> 
> This was in my original patch, but I decided to put a comment and keep
> the old  behavior. I probably will switch to a more precise reporting
> (per inuse ratio) in a separate patch, so that we can easily revert it
> without any impact on new fullness grouping.

Sounds good.