From: Goffredo Baroncelli <kreijack@inwind.it>
To: Anand Jain <Anand.Jain@oracle.com>
Cc: dsterba@suse.cz, Chris Mason <clm@fb.com>,
Miao Xie <miaox@cn.fujitsu.com>,
linux-btrfs@vger.kernel.org
Subject: Re: [PATCH RFC 0/5] Scan all devices to build fs device list
Date: Mon, 08 Sep 2014 19:15:19 +0200 [thread overview]
Message-ID: <540DE427.4040008@inwind.it> (raw)
In-Reply-To: <540D8D45.6000608@oracle.com>
On 09/08/2014 01:04 PM, Anand Jain wrote:
>
>
> On 08/09/2014 17:09, David Sterba wrote:
>> On Sat, Sep 06, 2014 at 04:05:20PM -0400, Chris Mason wrote:
>>> On 09/03/2014 09:36 AM, Miao Xie wrote:
>>>> This patchset implements device list automatic building function. As we
>>>> know, currently we need scan the devices to build device list by a user tool
>>>> before mounting the filesystem, especially mount the filesystem after
>>>> we re-install btrfs module. It is not convenient. This patchset can improve
>>>> that problem. With this patchset, we will scan all the devices in the
>>>> system to build the device list if we find the number of the devices
>>>> is not right when we mount the filesystem. By this way, we needn't scan
>>>> the device by the user tool and reduce the mount failure probability due
>>>> to the incomplete device list.
>>>
>>> Thanks for working on these patches, but I really prefer that we do
>>> these scans from userspace.
>>
>> I agree. The userspace approach gives more control of when and how the
>> scanning is done. Yes the scan has to be done after the module is
>> inserted, but distros have that in initrd. Reinstalling module is not
>> something a normal user does and developers know how to workaround.
>>
>> Automatic scanning in usperspace can be done via the mount helper and
>> this is IMO the way to go. There's a patch for that from Goffredo, not
>> merged yet, the patch backlog is still too long.
>
>
> Since we are on the topic of scanning. A point on improving the
> btrfs-progs scan method which I am working on...
>
> - Scan of all system devices is an expensive task. But btrfs-progs
> do it very liberally. Due to this there are some serious problem
> like - btrfs fi show is too slow when scrub is running.
>
> - The worst is Single btrfs-progs thread scans for btrfs
> devices multiple times. Mainly because most of the functions
> uses check_mounted() which in turn calls scan, think of
> multi device btrfs config.
Using libblkid (see your proposal below) would help in this case,
because the values would be cached.
>
> - The problem would be more prominent in larger server with 1000's
> of LUNs / devices.
>
> - lblkid can be the only method to scan for devices. (The other
> method we have as of now is of canning /proc/partitions, which
> lblkid also does).
>
> what I am planning -
> Use btrfs control ioctl to help btrfs-progs check_mounted() to know
> if a (multi) device is mounted.
> Build kernel's fs_devices list in the user-space using btrfs
> control ioctl.
> Do device scan only once per btrfs-progs thread.
You are talking about a ioctl: why not use (extending them when needed)
the sysfs information ?
>
> Any comments ?
>
> Thanks, Anand
>
>
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--
gpg @keyserver.linux.it: Goffredo Baroncelli (kreijackATinwind.it>
Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5
next prev parent reply other threads:[~2014-09-08 17:08 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-03 13:36 [PATCH RFC 0/5] Scan all devices to build fs device list Miao Xie
2014-09-03 13:36 ` [PATCH 1/5] block: export disk_class and disk_type for btrfs Miao Xie
2014-09-03 13:36 ` [PATCH 2/5] Btrfs: don't return btrfs_fs_devices if the caller doesn't want it Miao Xie
2014-09-03 13:36 ` [PATCH 3/5] Btrfs: restructure btrfs_scan_one_device Miao Xie
2014-09-03 13:36 ` [PATCH 4/5] Btrfs: restructure btrfs_get_bdev_and_sb and pick up some code used later Miao Xie
2014-09-03 13:36 ` [PATCH 5/5] Btrfs: scan all the devices and build the fs device list by btrfs's self Miao Xie
2014-09-06 11:48 ` Goffredo Baroncelli
2014-09-09 4:06 ` Miao Xie
2014-09-06 20:05 ` [PATCH RFC 0/5] Scan all devices to build fs device list Chris Mason
2014-09-08 9:09 ` David Sterba
2014-09-08 11:04 ` Anand Jain
2014-09-08 17:15 ` Goffredo Baroncelli [this message]
2014-09-09 3:26 ` Anand Jain
2014-09-09 20:31 ` Goffredo Baroncelli
2014-09-10 6:06 ` Anand Jain
2014-09-08 16:59 ` Goffredo Baroncelli
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