linux-kernel - Re: [PATCH v5 00/21] mm/zsmalloc: add zpdesc memory descriptor for zswap.zpool

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Message-ID: <20240807051754.GA428000@google.com>
Date: Wed, 7 Aug 2024 14:17:54 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Yosry Ahmed <yosryahmed@...gle.com>,
	Matthew Wilcox <willy@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, alexs@...nel.org,
	Vitaly Wool <vitaly.wool@...sulko.com>,
	Miaohe Lin <linmiaohe@...wei.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, minchan@...nel.org, senozhatsky@...omium.org,
	david@...hat.com, 42.hyeyoo@...il.com, nphamcs@...il.com
Subject: Re: [PATCH v5 00/21] mm/zsmalloc: add zpdesc memory descriptor for
 zswap.zpool

On (24/08/06 12:34), Yosry Ahmed wrote:
[..]
> > So the sole reason for this work is as a part of the mem_desc
> > conversion.  I'd like to hear from others who are to be involved in
> > that conversion, please - it this patchset something we should be
> > merging?
> >
> 
> Matthew asked an important question here that needs to be answered by
> zsmalloc experts:
> https://lore.kernel.org/lkml/Zq0zucMFsOwATsAC@casper.infradead.org/

Iff "zsmalloc experts" include me: I was under impression that there was
a zsmalloc conversion plan otherwise this zpdesc effort is a little
confusing, and, frankly, it hasn't appeared to me that this is "my problem"
now.

> Do you allocate a per-page struct zpdesc, and have each one pointing
> to a zspage?

I'm not very knowledgeable when it comes to memdesc, excuse my
ignorance, and please feel free to educate me.

So I guess if we have something

struct zspage {
	..
	struct zpdesc *first_desc;
	..
}

and we "chain" zpdesc-s to form a zspage, and make each of them point to
a corresponding struct page (memdesc -> *page), then it'll resemble current
zsmalloc and should work for everyone? I also assume for zspdesc-s zsmalloc
will need to maintain a dedicated kmem_cache?