linux-kernel - Re: [PATCH/RFC] VFS: don't keep disconnected dentries on d

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Message-ID: <20171220225604.GA2980@bombadil.infradead.org>
Date:   Wed, 20 Dec 2017 14:56:04 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     NeilBrown <neilb@...e.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        Anna Schumaker <Anna.Schumaker@...app.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>
Subject: Re: [PATCH/RFC] VFS: don't keep disconnected dentries on d_anon

On Thu, Dec 21, 2017 at 09:45:40AM +1100, NeilBrown wrote:
> -c/ Helper routines to allocate anonymous dentries, and to help attach
> +   prefix.  If the refcount on a dentry with this flag set
> +   becomes zero, the dentry is immediately discarded, rather than being
> +   kept in the dcache.  If a dentry that is not already in the dcache
> +   is repeatedly accessed by filehandle (as NFSD might do), an new dentry
> +   will be a allocated for each access, and discarded at the end of

s/a //

> +   the access.  As there is no parent, children, or name in the dentry
> +   is it unlikely that there will be any useful information to lose,
> +   and allocating a new dentry should normally be fast.

How about:

As the dentry is completely unattached, there is little information to
lose, and allocating a new dentry is normally fast.