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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Sat, 14 Jul 2018 11:00:32 -0700
Message-ID: <CA+55aFw1vrsTjJyoq4Q3jBwv1nXaTkkmSbHO6vozWZuTc7_6Kg@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
List-ID: <linux-mm.kvack.org>
To: Pavel Machek <pavel@ucw.cz>
Cc: Jan Kara <jack@suse.cz>, Andrew Morton <akpm@linux-foundation.org>, James Bottomley <James.Bottomley@hansenpartnership.com>, Waiman Long <longman@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>, 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 10:35 AM Pavel Machek <pavel@ucw.cz> wrote:
>
> Could we allocate -ve entries from separate slab?

No, because negative dentrires don't stay negative.

Every single positive dentry starts out as a negative dentry that is
passed in to "lookup()" to maybe be made positive.

And most of the time they <i>do</i> turn positive, because most of the
time people actually open files that exist.

But then occasionally you don't, because you're just blindly opening a
filename whether it exists or not (to _check_ whether it's there).

              Linus