linux-kernel - [discussion] proposal to bypass zero data for dm-crypt

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Message-ID: <73152f2b-2a3e-37a7-4578-9a4ae7ec903f@huaweicloud.com>
Date: Sat, 21 Dec 2024 10:34:05 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Alasdair Kergon <agk@...hat.com>, Mike Snitzer <snitzer@...nel.org>,
 Mikulas Patocka <mpatocka@...hat.com>, dm-devel@...ts.linux.dev,
 lkml <linux-kernel@...r.kernel.org>, "yukuai (C)" <yukuai3@...wei.com>
Subject: [discussion] proposal to bypass zero data for dm-crypt

Background

We provide virtual machines for customers to use, which include an 
important feature: in the initial state, the disks in the virtual 
machine do not occupy actual storage space, and the data read by users 
is all zeros until the user writes data for the first time. This can 
save a large amount of storage.

Problem

However, after introducing dm-crypt, this feature has failed. Because we 
expect the data read by users in the initial state to be zero, we have 
to write all zeros from dm-crypt.

Hence we'd like to propose to bypass zero data for dm-crypt, for
example:

before:
zero data -> encrypted zero data
decrypted zero data -> zero data
others

after:
zero data -> zero data
decrypted zero data -> encrypted zero data
others(doesn't change)

We'd like to hear from the community for suggestions first, before we
start. :)

Thanks,
Kuai