linux-kernel - Re: [RFC PATCHv5 0/6] zram: introduce writeback bio batching

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Message-ID: <2c6906d1-132e-401f-830f-ae771fe836c5@linux.alibaba.com>
Date: Sat, 22 Nov 2025 22:09:15 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: Sergey Senozhatsky <senozhatsky@...omium.org>
Cc: Yuwen Chen <ywen.chen@...mail.com>, akpm@...ux-foundation.org,
 bgeffon@...gle.com, licayy@...look.com, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org, minchan@...nel.org,
 richardycc@...gle.com
Subject: Re: [RFC PATCHv5 0/6] zram: introduce writeback bio batching



On 2025/11/22 21:43, Sergey Senozhatsky wrote:
> On (25/11/22 20:24), Gao Xiang wrote:
>> zram(ext4) means zram device itself is formated as ext4.
>>
>>>
>>>> zram(ext4) -> backing ext4/btrfs
>>>
>>> This is not a valid configuration, as far as I'm concerned.
>>> Unless I'm missing your point.
>>
>> Why it's not valid? zram can be used as a regular virtual
>> block device, and format with any fs, and mount the zram
>> then.
> 
> I thought you were talking about the backing device being
> ext4/btrfs.  Sorry, I don't have enough context/knowledge
> to understand what you're getting at.  zram has been doing
> writeback for ages, I really don't know what you mean by
> "to act like this".

I mean, if zram is formatted as ext4, and then mount it;
and then there is a backing file which is also in another
ext4, you'd need a workqueue to do writeback I/Os (or needs
a loop device to transit), was that the original question
raised by Yuwen?

If it's backed by a physical device rather than a file in
a filesystem, such potential problem doesn't exist.

Thanks,
Gao Xiang