linux-kernel - Re: [PATCH v5 4/4] mm: Introduce per-thpsize swapin control policy

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Message-ID: <ZqkVMpbl5pH35uOq@infradead.org>
Date: Tue, 30 Jul 2024 09:30:42 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Barry Song <21cnbao@...il.com>
Cc: Christoph Hellwig <hch@...radead.org>,
	Matthew Wilcox <willy@...radead.org>, akpm@...ux-foundation.org,
	linux-mm@...ck.org, ying.huang@...el.com,
	baolin.wang@...ux.alibaba.com, chrisl@...nel.org, david@...hat.com,
	hannes@...xchg.org, hughd@...gle.com, kaleshsingh@...gle.com,
	kasong@...cent.com, linux-kernel@...r.kernel.org, mhocko@...e.com,
	minchan@...nel.org, nphamcs@...il.com, ryan.roberts@....com,
	senozhatsky@...omium.org, shakeel.butt@...ux.dev,
	shy828301@...il.com, surenb@...gle.com, v-songbaohua@...o.com,
	xiang@...nel.org, yosryahmed@...gle.com
Subject: Re: [PATCH v5 4/4] mm: Introduce per-thpsize swapin control policy

On Tue, Jul 30, 2024 at 08:11:16AM +1200, Barry Song wrote:
> > We also really need to stop optimizing for this weird zram case and move
> > people to zswap instead after fixing the various issues.  A special
> > block device that isn't really a block device and needs various special
> > hooks isn't the right abstraction for different zwap strategies.
> 
> My understanding is zRAM is much more popularly used in embedded
> systems than zswap. I seldomly(or never) hear who is using zswap
> in Android. it seems pointless to force people to move to zswap, in
> embedded systems we don't have a backend real block disk device
> after zswap.

Well, that is the point.  zram is a horrible hack that abuses a block
device to implement a feature missing the VM layer.  Right now people
have a reason for it because zswap requires a "real" backing device
and that's fine for them and for now.  But instead of building VM
infrastructure around these kinds of hacks we need to fix the VM
infrastructure.  Chris Li has been talking about and working towards
a proper swap abstraction and that needs to happen.