On Thu, Feb 23, 2023 at 05:09:14PM +0100, Christian Brauner wrote: > 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. Size limits is just one bell, in fact ramfs has no configurable options. So in fact *all* options parsed on shmem_parse_options() are only available with tmpfs, some of the options are: * size * number of blocks * number of inodes * NUMA memory allocation policy * huge pages > 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. I guess its time to update Documentation/filesystems/tmpfs.rst. Luis
