linux-kernel - Re: [RFC PATCH v2 00/21] mm/zsmalloc: Split zsdesc from struct page

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Message-ID: <20230720071826.GE955071@google.com>
Date:   Thu, 20 Jul 2023 16:18:26 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc:     Minchan Kim <minchan@...nel.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Matthew Wilcox <willy@...radead.org>,
        Mike Rapoport <rppt@...nel.org>
Subject: Re: [RFC PATCH v2 00/21] mm/zsmalloc: Split zsdesc from struct page

On (23/07/13 13:20), Hyeonggon Yoo wrote:
> The purpose of this series is to define own memory descriptor for zsmalloc,
> instead of re-using various fields of struct page. This is a part of the
> effort to reduce the size of struct page to unsigned long and enable
> dynamic allocation of memory descriptors.
> 
> While [1] outlines this ultimate objective, the current use of struct page
> is highly dependent on its definition, making it challenging to separately
> allocate memory descriptors.

I glanced through the series and it all looks pretty straight forward to
me. I'll have a closer look. And we definitely need Minchan to ACK it.

> Therefore, this series introduces new descriptor for zsmalloc, called
> zsdesc. It overlays struct page for now, but will eventually be allocated
> independently in the future.

So I don't expect zsmalloc memory usage increase. On one hand for each
physical page that zspage consists of we will allocate zsdesc (extra bytes),
but at the same time struct page gets slimmer. So we should be even, or
am I wrong?