linux-kernel - Re: [PATCHv4 8/9] Documentation: document zram pages_per_pool

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Message-ID: <Y24lMtZc5tlxVObM@google.com>
Date:   Fri, 11 Nov 2022 19:34:26 +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>,
        Nitin Gupta <ngupta@...are.org>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCHv4 8/9] Documentation: document zram pages_per_pool_page
 attribute

On (22/11/10 18:20), Minchan Kim wrote:
> > diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
> > index 010fb05a5999..4cb287520d45 100644
> > --- a/Documentation/admin-guide/blockdev/zram.rst
> > +++ b/Documentation/admin-guide/blockdev/zram.rst
> > @@ -112,7 +112,29 @@ to list all of them using, for instance, /proc/crypto or any other
> >  method. This, however, has an advantage of permitting the usage of
> >  custom crypto compression modules (implementing S/W or H/W compression).
> >  
> > -4) Set Disksize
> > +4) Set pages per-pool page limit: Optional
> > +==========================================
> > +
> > +zsmalloc pages can consist of up to ZS_DEFAULT_PAGES_PER_ZSPAGE (single)
> > +physical pages. The exact number is calculated for each zsmalloc size
> > +class during zsmalloc pool creation. ZRAM provides pages_per_pool_page
> > +device attribute that lets one adjust that limit (maximum possible value
> > +is ZS_MAX_PAGES_PER_ZSPAGE). The default limit is considered to be good
> > +enough, so tweak this value only when the changes in zsmalloc size classes
> > +characteristics are beneficial for your data patterns. The limit on the
> > +pages per zspages (currently) should be in [1,16] range; default value
> > +is 4.
> 
> I think we need to introudce pros and cons for user to decide it since
> it's not familiar with admin. I think It would need more explanation about
> zsmalloc internal(especailly zspage and size classes)

OK, agreed. I have quite a bit of info in the 0002 commit messages.
I can copy-paste some of those bits and edit them. We also have
some info the internal doc, which I can also use as a "source of
inspiration".