linux-kernel - Re: [PATCHv2 0/4] zsmalloc: make zspage chain size configurable

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Message-ID: <Y8I9MAd0zjvR0sQe@google.com>
Date:   Sat, 14 Jan 2023 14:27:12 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv2 0/4] zsmalloc: make zspage chain size configurable

On (23/01/13 11:57), Mike Kravetz wrote:
> > 	This turns hard coded limit on maximum number of physical
> > pages per-zspage into a config option. It also increases the default
> > limit from 4 to 8.
> > 
> > Sergey Senozhatsky (4):
> >   zsmalloc: rework zspage chain size selection
> >   zsmalloc: skip chain size calculation for pow_of_2 classes
> >   zsmalloc: make zspage chain size configurable
> >   zsmalloc: set default zspage chain size to 8
> > 
> >  Documentation/mm/zsmalloc.rst | 168 ++++++++++++++++++++++++++++++++++
> >  mm/Kconfig                    |  19 ++++
> >  mm/zsmalloc.c                 |  72 +++++----------
> >  3 files changed, 212 insertions(+), 47 deletions(-)
> 
> Hi Sergey,

Hi Mike,

> The following BUG shows up after this series in linux-next.  I can easily
> recreate by doing the following:
>
> # echo large_value > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
> where 'large_value' is a so big that there could never possibly be that
> many 2MB huge pages in the system.

Hmm... Are we sure this is related? I really cannot see how chain-size
can have an effect on zspage ->isolate counter. What chain-size value
do you use? You don't see problems with chain size of 4?