linux-ext4 - Re: Transparent compression with ext4

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <Z5D8q3QtpNiGSo22@infradead.org>
Date: Wed, 22 Jan 2025 06:11:55 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Theodore Ts'o <tytso@....edu>
Cc: Christoph Hellwig <hch@...radead.org>,
	Gerhard Wiesinger <lists@...singer.com>, linux-ext4@...r.kernel.org
Subject: Re: Transparent compression with ext4 - especially with zstd

On Wed, Jan 22, 2025 at 08:19:12AM -0500, Theodore Ts'o wrote:
> ... but out of place writes means that every single fdatasync() called
> by the database now requires a file system level transaction commits.

Yes.

> So now every single fdatasync(2) results in the data blocks getting
> written out to a new location on disk (this is what out of place
> writes mean), followed by a CACHE FLUSH, followed by the metadata
> updates to point at the new location on the disk, first written to the
> file system tranaction log, followed by the fs commit block, followed
> by a *second* CACHE FLUSH command.

Or you put the compressed data in the log and have a single FUA
write.