Re: [PATCH v5 0/6] fs/dcache: Track & limit # of negative dentries

[Linus Torvalds]

On Sat, Jul 14, 2018 at 11:36 AM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
>
> OK, this
>         /*
>          * No ordinary (disk based) filesystem counts links as inodes;
>          * but each new link needs a new dentry, pinning lowmem, and
>          * tmpfs dentries cannot be pruned until they are unlinked.
>          */
>         ret = shmem_reserve_inode(inode->i_sb);
>         if (ret)
>                 goto out;
> will probably help (on ramfs it won't, though).

Nobody who cares about memory use would use ramfs and then allow
random users on it.

I think you can exhaust memory more easily on ramfs by just writing a
huge file. Do we have any limits at all?

ramfs is fine for things like initramfs, but I think the comment says it all:

 * NOTE! This filesystem is probably most useful
 * not as a real filesystem, but as an example of
 * how virtual filesystems can be written.

and even that comment may have been more correct back in 2000 than it is today.

             Linus