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

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Date:   Sat, 14 Jul 2018 11:43:57 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Pavel Machek <pavel@....cz>, Jan Kara <jack@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Waiman Long <longman@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Larry Woodman <lwoodman@...hat.com>,
        "Wangkai (Kevin,C)" <wangkai86@...wei.com>,
        linux-mm <linux-mm@...ck.org>, Michal Hocko <mhocko@...nel.org>
Subject: Re: [PATCH v5 0/6] fs/dcache: Track & limit # of negative dentries

On Sat, Jul 14, 2018 at 11:36 AM Al Viro <viro@...iv.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