| Message ID | 20200616021737.44617-2-wqu@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | btrfs: workaround exhausted anonymous block device pool | expand |
On 6/15/20 10:17 PM, Qu Wenruo wrote: > [BUG] > When a lot of subvolumes are created, there is a user report about > transaction aborted: > > ------------[ cut here ]------------ > BTRFS: Transaction aborted (error -24) > WARNING: CPU: 17 PID: 17041 at fs/btrfs/transaction.c:1576 create_pending_snapshot+0xbc4/0xd10 [btrfs] > RIP: 0010:create_pending_snapshot+0xbc4/0xd10 [btrfs] > Call Trace: > create_pending_snapshots+0x82/0xa0 [btrfs] > btrfs_commit_transaction+0x275/0x8c0 [btrfs] > btrfs_mksubvol+0x4b9/0x500 [btrfs] > btrfs_ioctl_snap_create_transid+0x174/0x180 [btrfs] > btrfs_ioctl_snap_create_v2+0x11c/0x180 [btrfs] > btrfs_ioctl+0x11a4/0x2da0 [btrfs] > do_vfs_ioctl+0xa9/0x640 > ksys_ioctl+0x67/0x90 > __x64_sys_ioctl+0x1a/0x20 > do_syscall_64+0x5a/0x110 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > ---[ end trace 33f2f83f3d5250e9 ]--- > BTRFS: error (device sda1) in create_pending_snapshot:1576: errno=-24 unknown > BTRFS info (device sda1): forced readonly > BTRFS warning (device sda1): Skipping commit of aborted transaction. > BTRFS: error (device sda1) in cleanup_transaction:1831: errno=-24 unknown > > [CAUSE] > The root cause is we don't have unlimited resource for anonymous block > device number. > The anonymous block device pool only contains 1<<20 devices, and is > shared across a several fses, like ceph and overlayfs. > > While btrfs has support for 1<<48 subvolumes, so it's just a problem of > time to hit such limit. > > [WORKAROUND] > Since it's not possible to completely solve the problem, we can only > workaround it. > > Firstly, we can reduce the user of anon_dev. Data reloc tree is not visible > to users, thus it doesn't need anon_dev at all. > > This patch will do extra check on root objectid, to rule out roots who > don't need anon_dev. > Although currently it's only data reloc tree and orphan roots. > > Reported-by: Greed Rong <greedrong@gmail.com> > Link: https://lore.kernel.org/linux-btrfs/CA+UqX+NTrZ6boGnWHhSeZmEY5J76CTqmYjO2S+=tHJX7nb9DPw@mail.gmail.com/ > Signed-off-by: Qu Wenruo <wqu@suse.com> Reviewed-by: Josef Bacik <josef@toxicpanda.com> Thanks, Josef
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index c70d47b8090a..cfc0ff288238 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -1428,9 +1428,17 @@ static int btrfs_init_fs_root(struct btrfs_root *root) spin_lock_init(&root->ino_cache_lock); init_waitqueue_head(&root->ino_cache_wait); - ret = get_anon_bdev(&root->anon_dev); - if (ret) - goto fail; + /* + * Anonymous block device pool has limited size (1M), which is way + * smaller than btrfs subvolumes limits (1<<48). + * We shouldn't allocate any if it's not a user visible subvolume. + */ + if (is_fstree(root->root_key.objectid) && + btrfs_root_refs(&root->root_item)) { + ret = get_anon_bdev(&root->anon_dev); + if (ret) + goto fail; + } mutex_lock(&root->objectid_mutex); ret = btrfs_find_highest_objectid(root,
[BUG] When a lot of subvolumes are created, there is a user report about transaction aborted: ------------[ cut here ]------------ BTRFS: Transaction aborted (error -24) WARNING: CPU: 17 PID: 17041 at fs/btrfs/transaction.c:1576 create_pending_snapshot+0xbc4/0xd10 [btrfs] RIP: 0010:create_pending_snapshot+0xbc4/0xd10 [btrfs] Call Trace: create_pending_snapshots+0x82/0xa0 [btrfs] btrfs_commit_transaction+0x275/0x8c0 [btrfs] btrfs_mksubvol+0x4b9/0x500 [btrfs] btrfs_ioctl_snap_create_transid+0x174/0x180 [btrfs] btrfs_ioctl_snap_create_v2+0x11c/0x180 [btrfs] btrfs_ioctl+0x11a4/0x2da0 [btrfs] do_vfs_ioctl+0xa9/0x640 ksys_ioctl+0x67/0x90 __x64_sys_ioctl+0x1a/0x20 do_syscall_64+0x5a/0x110 entry_SYSCALL_64_after_hwframe+0x44/0xa9 ---[ end trace 33f2f83f3d5250e9 ]--- BTRFS: error (device sda1) in create_pending_snapshot:1576: errno=-24 unknown BTRFS info (device sda1): forced readonly BTRFS warning (device sda1): Skipping commit of aborted transaction. BTRFS: error (device sda1) in cleanup_transaction:1831: errno=-24 unknown [CAUSE] The root cause is we don't have unlimited resource for anonymous block device number. The anonymous block device pool only contains 1<<20 devices, and is shared across a several fses, like ceph and overlayfs. While btrfs has support for 1<<48 subvolumes, so it's just a problem of time to hit such limit. [WORKAROUND] Since it's not possible to completely solve the problem, we can only workaround it. Firstly, we can reduce the user of anon_dev. Data reloc tree is not visible to users, thus it doesn't need anon_dev at all. This patch will do extra check on root objectid, to rule out roots who don't need anon_dev. Although currently it's only data reloc tree and orphan roots. Reported-by: Greed Rong <greedrong@gmail.com> Link: https://lore.kernel.org/linux-btrfs/CA+UqX+NTrZ6boGnWHhSeZmEY5J76CTqmYjO2S+=tHJX7nb9DPw@mail.gmail.com/ Signed-off-by: Qu Wenruo <wqu@suse.com> --- fs/btrfs/disk-io.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-)