linux-kernel - Re: [PATCH 06/18] fsinfo: Add a uniquifier ID to struct mount [ver #21]

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Message-ID: <CAJfpegtOguKOGWxv-sA_C9eSWG_3Srnj_k=oW-wSHNprCipFVg@mail.gmail.com>
Date:   Wed, 5 Aug 2020 16:46:31 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     David Howells <dhowells@...hat.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ian Kent <raven@...maw.net>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Christian Brauner <christian@...uner.io>,
        Jann Horn <jannh@...gle.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Karel Zak <kzak@...hat.com>, Jeff Layton <jlayton@...hat.com>,
        Linux API <linux-api@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org,
        LSM <linux-security-module@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/18] fsinfo: Add a uniquifier ID to struct mount [ver #21]

On Wed, Aug 5, 2020 at 4:14 PM David Howells <dhowells@...hat.com> wrote:

> However, looking up that identifier requires some sort of structure for doing
> this and it's kind of worst case for the IDR tree as the keys are gradually
> going to spread out, causing it to eat more memory.  It may be a tradeoff
> worth making, and the memory consumption might not be that bad - or we could
> use some other data structure such as an rbtree.

idr_alloc_cyclic() seems to be a good template for doing the lower
32bit allocation, and we can add code to increment the high 32bit on
wraparound.

Lots of code uses idr_alloc_cyclic() so I guess it shouldn't be too
bad in terms of memory use or performance.

Thanks,
Miklos