linux-ext4 - Re: Transparent compression with ext4

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Message-ID: <Z5CgQosGsbxbbEIL@infradead.org>
Date: Tue, 21 Jan 2025 23:37:38 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Gerhard Wiesinger <lists@...singer.com>
Cc: Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org
Subject: Re: Transparent compression with ext4 - especially with zstd

On Wed, Jan 22, 2025 at 08:29:09AM +0100, Gerhard Wiesinger wrote:
> BTW: Why does it break the ACID properties?

It doesn't if implemented properly, which of course means out of place
writes.

The only sane way to implement compression in XFS would be using out
of place writes, which we support for reflinks and which is heavily
used by the new zoned mode.  For the latter retrofitting compression
would be relatively easy, but it first needs to get merged, then
stabilize and mature, and then we'll need to see if we have enough
use cases.  So don't plan for it.