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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Wed, 16 Jun 2021 11:12:36 +0200
Message-ID: <CAJfpegttf+kYBCLsUc9eFLc-KNaN=0smdSMoemAK6t52Kb=fEg@mail.gmail.com>
Subject: Re: [PATCH v7 3/6] kernfs: use VFS negative dentry caching
To:     Ian Kent <raven@themaw.net>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Tejun Heo <tj@kernel.org>, Eric Sandeen <sandeen@sandeen.net>,
        Fox Chen <foxhlchen@gmail.com>,
        Brice Goglin <brice.goglin@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Rick Lindsley <ricklind@linux.vnet.ibm.com>,
        David Howells <dhowells@redhat.com>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Carlos Maiolino <cmaiolino@redhat.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Tue, 15 Jun 2021 at 12:26, Ian Kent <raven@themaw.net> wrote:
>
> If there are many lookups for non-existent paths these negative lookups
> can lead to a lot of overhead during path walks.
>
> The VFS allows dentries to be created as negative and hashed, and caches
> them so they can be used to reduce the fairly high overhead alloc/free
> cycle that occurs during these lookups.
>
> Use the kernfs node parent revision to identify if a change has been
> made to the containing directory so that the negative dentry can be
> discarded and the lookup redone.
>
> Signed-off-by: Ian Kent <raven@themaw.net>

Reviewed-by: Miklos Szeredi <mszeredi@redhat.com>