From: "NeilBrown" <neilb@suse.de>
To: "Qu Wenruo" <quwenruo.btrfs@gmx.com>
Cc: "Zygo Blaxell" <ce3g8jdj@umail.furryterror.org>,
"Neal Gompa" <ngompa13@gmail.com>,
"Wang Yugui" <wangyugui@e16-tech.com>,
"Christoph Hellwig" <hch@infradead.org>,
"Josef Bacik" <josef@toxicpanda.com>,
"J. Bruce Fields" <bfields@fieldses.org>,
"Chuck Lever" <chuck.lever@oracle.com>,
"Chris Mason" <clm@fb.com>, "David Sterba" <dsterba@suse.com>,
"Alexander Viro" <viro@zeniv.linux.org.uk>,
"linux-fsdevel" <linux-fsdevel@vger.kernel.org>,
linux-nfs@vger.kernel.org,
"Btrfs BTRFS" <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH/RFC 00/11] expose btrfs subvols in mount table correctly
Date: Fri, 30 Jul 2021 16:00:54 +1000 [thread overview]
Message-ID: <162762485406.21659.16909119511605460065@noble.neil.brown.name> (raw)
In-Reply-To: <046c96cd-f2a5-be04-e7b5-012e896c5816@gmx.com>
On Fri, 30 Jul 2021, Qu Wenruo wrote:
>
> On 2021/7/30 下午1:25, Qu Wenruo wrote:
> >
> >
> > On 2021/7/30 上午10:36, NeilBrown wrote:
> >>
> >> I've been pondering all the excellent feedback, and what I have learnt
> >> from examining the code in btrfs, and I have developed a different
> >> perspective.
> >
> > Great! Some new developers into the btrfs realm!
> >
> >>
> >> Maybe "subvol" is a poor choice of name because it conjures up
> >> connections with the Volumes in LVM, and btrfs subvols are very different
> >> things. Btrfs subvols are really just subtrees that can be treated as a
> >> unit for operations like "clone" or "destroy".
> >>
> >> As such, they don't really deserve separate st_dev numbers.
> >>
> >> Maybe the different st_dev numbers were introduced as a "cheap" way to
> >> extend to size of the inode-number space. Like many "cheap" things, it
> >> has hidden costs.
>
> Forgot another problem already caused by this st_dev method.
>
> Since btrfs uses st_dev to distinguish them its inode name space, and
> st_dev is allocated using anonymous bdev, and the anonymous bdev poor
> has limited size (much smaller than btrfs subvolume id name space), it's
> already causing problems like we can't allocate enough anonymous bdev
> for each subvolume, and failed to create subvolume/snapshot.
What sort of numbers do you see in practice? How many subvolumes and how
many inodes per subvolume?
If we allocated some number of bits to each, with over-allocation to
allow for growth, could we fit both into 64 bits?
NeilBrown
>
> Thus it's really a time to re-consider how we should export this info to
> user space.
>
> Thanks,
> Qu
>
next prev parent reply other threads:[~2021-07-30 6:01 UTC|newest]
Thread overview: 122+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-27 22:37 [PATCH/RFC 00/11] expose btrfs subvols in mount table correctly NeilBrown
2021-07-27 22:37 ` [PATCH 07/11] exportfs: Allow filehandle lookup to cross internal mount points NeilBrown
2021-07-28 10:13 ` Amir Goldstein
2021-07-29 0:28 ` NeilBrown
2021-07-29 5:27 ` Amir Goldstein
2021-08-06 7:52 ` Miklos Szeredi
2021-08-06 8:08 ` Amir Goldstein
2021-08-06 8:18 ` Miklos Szeredi
2021-07-28 19:17 ` J. Bruce Fields
2021-07-28 22:25 ` NeilBrown
2021-07-27 22:37 ` [PATCH 04/11] VFS: export lookup_mnt() NeilBrown
2021-07-30 0:31 ` Al Viro
2021-07-30 5:33 ` NeilBrown
2021-07-27 22:37 ` [PATCH 01/11] VFS: show correct dev num in mountinfo NeilBrown
2021-07-30 0:25 ` Al Viro
2021-07-30 5:28 ` NeilBrown
2021-07-30 5:54 ` Miklos Szeredi
2021-07-30 6:13 ` NeilBrown
2021-07-30 7:18 ` Miklos Szeredi
2021-07-30 7:33 ` NeilBrown
2021-07-30 7:59 ` Miklos Szeredi
2021-08-02 4:18 ` A Third perspective on BTRFS nfsd subvol dev/inode number issues NeilBrown
2021-08-02 5:25 ` Al Viro
2021-08-02 5:40 ` NeilBrown
2021-08-02 7:54 ` Amir Goldstein
2021-08-02 13:53 ` Josef Bacik
2021-08-03 22:29 ` Qu Wenruo
2021-08-02 14:47 ` Frank Filz
2021-08-02 21:24 ` NeilBrown
2021-08-02 7:15 ` Martin Steigerwald
2021-08-02 21:40 ` NeilBrown
2021-08-02 12:39 ` J. Bruce Fields
2021-08-02 20:32 ` Patrick Goetz
2021-08-02 20:41 ` J. Bruce Fields
2021-08-02 21:10 ` NeilBrown
2021-08-02 21:50 ` J. Bruce Fields
2021-08-02 21:59 ` NeilBrown
2021-08-02 22:14 ` J. Bruce Fields
2021-08-02 22:36 ` NeilBrown
2021-08-03 0:15 ` J. Bruce Fields
2021-07-27 22:37 ` [PATCH 03/11] VFS: pass lookup_flags into follow_down() NeilBrown
2021-07-27 22:37 ` [PATCH 11/11] btrfs: use automount to bind-mount all subvol roots NeilBrown
2021-07-28 8:37 ` kernel test robot
2021-07-28 8:37 ` [RFC PATCH] btrfs: btrfs_mountpoint_expiry_timeout can be static kernel test robot
2021-07-28 13:12 ` [PATCH 11/11] btrfs: use automount to bind-mount all subvol roots Christian Brauner
2021-07-29 0:43 ` NeilBrown
2021-07-29 14:38 ` Christian Brauner
2021-07-31 6:25 ` [btrfs] 5874902268: xfstests.btrfs.202.fail kernel test robot
2021-07-27 22:37 ` [PATCH 06/11] nfsd: include a vfsmount in struct svc_fh NeilBrown
2021-07-27 22:37 ` [PATCH 10/11] btrfs: introduce mapping function from location to inum NeilBrown
2021-07-27 22:37 ` [PATCH 02/11] VFS: allow d_automount to create in-place bind-mount NeilBrown
2021-07-27 22:37 ` [PATCH 09/11] nfsd: Allow filehandle lookup to cross internal mount points NeilBrown
2021-07-28 19:15 ` J. Bruce Fields
2021-07-28 22:29 ` NeilBrown
2021-07-30 0:42 ` Al Viro
2021-07-30 5:43 ` NeilBrown
2021-07-27 22:37 ` [PATCH 08/11] nfsd: change get_parent_attributes() to nfsd_get_mounted_on() NeilBrown
2021-07-27 22:37 ` [PATCH 05/11] VFS: new function: mount_is_internal() NeilBrown
2021-07-28 2:16 ` Al Viro
2021-07-28 3:32 ` NeilBrown
2021-07-30 0:34 ` Al Viro
2021-07-28 2:19 ` [PATCH/RFC 00/11] expose btrfs subvols in mount table correctly Al Viro
2021-07-28 4:58 ` Wang Yugui
2021-07-28 6:04 ` Wang Yugui
2021-07-28 7:01 ` NeilBrown
2021-07-28 12:26 ` Neal Gompa
2021-07-28 19:14 ` J. Bruce Fields
2021-07-29 1:29 ` Zygo Blaxell
2021-07-29 1:43 ` NeilBrown
2021-07-29 23:20 ` Zygo Blaxell
2021-07-28 22:50 ` NeilBrown
2021-07-29 2:37 ` Zygo Blaxell
2021-07-29 3:36 ` NeilBrown
2021-07-29 23:20 ` Zygo Blaxell
2021-07-30 2:36 ` NeilBrown
2021-07-30 5:25 ` Qu Wenruo
2021-07-30 5:31 ` Qu Wenruo
2021-07-30 5:53 ` Amir Goldstein
2021-07-30 6:00 ` NeilBrown [this message]
2021-07-30 6:09 ` Qu Wenruo
2021-07-30 5:58 ` NeilBrown
2021-07-30 6:23 ` Qu Wenruo
2021-07-30 6:53 ` NeilBrown
2021-07-30 7:09 ` Qu Wenruo
2021-07-30 18:15 ` Zygo Blaxell
2021-07-30 15:17 ` J. Bruce Fields
2021-07-30 15:48 ` Josef Bacik
2021-07-30 16:25 ` Forza
2021-07-30 17:43 ` Zygo Blaxell
2021-07-30 5:28 ` Amir Goldstein
2021-07-28 13:43 ` g.btrfs
2021-07-29 1:39 ` NeilBrown
2021-07-29 9:28 ` Graham Cobb
2021-07-28 7:06 ` NeilBrown
2021-07-28 9:36 ` Wang Yugui
2021-07-28 19:35 ` J. Bruce Fields
2021-07-28 21:30 ` Josef Bacik
2021-07-30 0:13 ` Al Viro
2021-07-30 6:08 ` NeilBrown
2021-08-13 1:45 ` [PATCH] VFS/BTRFS/NFSD: provide more unique inode number for btrfs export NeilBrown
2021-08-13 14:55 ` Josef Bacik
2021-08-15 7:39 ` Goffredo Baroncelli
2021-08-15 19:35 ` Roman Mamedov
2021-08-15 21:03 ` Goffredo Baroncelli
2021-08-15 21:53 ` NeilBrown
2021-08-17 19:34 ` Goffredo Baroncelli
2021-08-17 21:39 ` NeilBrown
2021-08-18 17:24 ` Goffredo Baroncelli
2021-08-15 22:17 ` NeilBrown
2021-08-19 8:01 ` Amir Goldstein
2021-08-20 3:21 ` NeilBrown
2021-08-20 6:23 ` Amir Goldstein
2021-08-23 4:05 ` [PATCH v2] BTRFS/NFSD: " NeilBrown
2021-08-18 14:54 ` [PATCH] VFS/BTRFS/NFSD: " Wang Yugui
2021-08-18 21:46 ` NeilBrown
2021-08-19 2:19 ` Zygo Blaxell
2021-08-20 2:54 ` NeilBrown
2021-08-22 19:29 ` Zygo Blaxell
2021-08-23 5:51 ` NeilBrown
2021-08-23 23:22 ` NeilBrown
2021-08-25 2:06 ` Zygo Blaxell
2021-08-23 0:57 ` Wang Yugui
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