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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Sat, 14 Jul 2018 11:43:57 -0700
Message-ID: <CA+55aFwPcoWFxgHb2TYGO3Mh2WyPfkhpwNAw7xxbar=ncb3Nuw@mail.gmail.com>
Subject: Re: [PATCH v5 0/6] fs/dcache: Track & limit # of negative dentries
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Sender: owner-linux-mm@kvack.org
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To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Pavel Machek <pavel@ucw.cz>, Jan Kara <jack@suse.cz>, Andrew Morton <akpm@linux-foundation.org>, James Bottomley <James.Bottomley@hansenpartnership.com>, Waiman Long <longman@redhat.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, Paul McKenney <paulmck@linux.vnet.ibm.com>, Ingo Molnar <mingo@kernel.org>, Miklos Szeredi <mszeredi@redhat.com>, Matthew Wilcox <willy@infradead.org>, Larry Woodman <lwoodman@redhat.com>, "Wangkai (Kevin,C)" <wangkai86@huawei.com>, linux-mm <linux-mm@kvack.org>, Michal Hocko <mhocko@kernel.org>

On Sat, Jul 14, 2018 at 11:36 AM Al Viro <viro@zeniv.linux.org.uk> 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