Re: [RFC v2 5/5] shmem: add support to ignore swap

Christian Brauner
2023-02-23T12:26:49Z

On Wed, Feb 22, 2023 at 06:44:12PM -0800, Luis Chamberlain wrote:
> In doing experimentations with shmem having the option to avoid swap
> becomes a useful mechanism. One of the *raves* about brd over shmem is
> you can avoid swap, but that's not really a good reason to use brd if
> we can instead use shmem. Using brd has its own good reasons to exist,
> but just because "tmpfs" doesn't let you do that is not a great reason
> to avoid it if we can easily add support for it.
>
> I don't add support for reconfiguring incompatible options, but if
> we really wanted to we can add support for that.
>
> To avoid swap we use mapping_set_unevictable() upon inode creation,
> and put a WARN_ON_ONCE() stop-gap on writepages() for reclaim.
>
> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
> ---

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,

Acked-by: Christian Brauner <brauner@kernel.org>