On Thu, Feb 23, 2023 at 07:16:09AM -0800, Christoph Hellwig wrote: > On Thu, Feb 23, 2023 at 01:26:31PM +0100, Christian Brauner wrote: > > We would have use-cases for this in systemd. We currently use ramfs for > > systemd's credential logic since ramfs is unswappable. It'd be very neat > > if we could use tmpfs instead, > > What is the advantage of using a swapless tmpfs over ramf? There are a few reasons we usually prefer tmpfs over ramfs. Iirc, ramfs doesn't have limits and grows dynamically. So we currently only use it from the most privileged process where we do our own accounting and immediately remount the superblock read-only. Tmpfs on the other hand offers various ways to restrict memory consumption. Other reasons are that ramfs doesn't support selinux labels, xattrs, and acls in general which come in quite handy. Starting with kernel v6.3 tmpfs does also support idmapped mounts. So we usually always prefer ramfs over tmpfs unless we have a very specific need such as the memory not being swapped out.
