linux-kernel - Re: [PATCH RFC] mm: ghost swapfile support for zswap

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Message-ID: <340fd55d9d7d9436f18205bb458e9bd469b36c6c.camel@surriel.com>
Date: Mon, 24 Nov 2025 11:14:29 -0500
From: Rik van Riel <riel@...riel.com>
To: Chris Li <chrisl@...nel.org>, Johannes Weiner <hannes@...xchg.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Kairui Song
 <kasong@...cent.com>,  Kemeng Shi <shikemeng@...weicloud.com>, Nhat Pham
 <nphamcs@...il.com>, Baoquan He <bhe@...hat.com>,  Barry Song
 <baohua@...nel.org>, Yosry Ahmed <yosry.ahmed@...ux.dev>, Chengming Zhou	
 <chengming.zhou@...ux.dev>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, 	pratmal@...gle.com, sweettea@...gle.com,
 gthelen@...gle.com, weixugc@...gle.com
Subject: Re: [PATCH RFC] mm: ghost swapfile support for zswap

On Fri, 2025-11-21 at 17:52 -0800, Chris Li wrote:
> On Fri, Nov 21, 2025 at 3:40 AM Johannes Weiner <hannes@...xchg.org>
> wrote:
> > 
> > 
> > Zswap is primarily a compressed cache for real swap on secondary
> > storage. It's indeed quite important that entries currently in
> > zswap
> > don't occupy disk slots; but for a solution to this to be
> > acceptable,
> > it has to work with the primary usecase and support disk writeback.
> 
> Well, my plan is to support the writeback via swap.tiers.
> 
How would you do writeback from a zswap entry in
a ghost swapfile, to a real disk swap backend?

That is the use case people are trying to solve.

How would your architecture address it?

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