On 18.11.2010 16:54, Chris Mason wrote:
Excerpts from Tomasz Chmielewski's message of 2010-11-18 10:39:05 -0500:
On 18.11.2010 16:07, Chris Mason wrote:
(...)
[27821.906513] btrfs-cache-8 D ffff88050c5fde98 0 8089 2 0x00000000
[27821.906517] ffff88051c3a9b60 0000000000000046 ffff88051c3a9b00 ffff88051c3a9fd8
[27821.906522] 00000000000139c0 00000000000139c0 ffff88051c3a9fd8 ffff88051c3a9fd8
[27821.906526] 00000000000139c0 ffff88050c5fde98 ffff88050c5fdea0 ffff88050c5fdb00
[27821.906530] Call Trace:
[27821.906534] [<ffffffff8159fc4e>] io_schedule+0x5e/0xa0
[27821.906538] [<ffffffff81109f15>] sync_page+0x45/0x60
So, you're caching block groups. What you want to do is use Josef's new
block group caching code.
mount -o space_cache /dev/xxx
Do the test and let the caching threads finish, then unmount and then
your next run should be fast.
# mount -o space_cache /dev/sdb4 /mnt/btrfs/
[29720.305741] btrfs: enabling disk space caching
[29720.305743] btrfs: force clearing of disk cache
I don't see any difference in behaviour with this mount option; it still
"hangs" for quite a bit at around ~1.8 GB (and reading with ~500 kB/s
when the hangs happens) on a subsequent dd run (several runs,
unmounts/mounts).
Right, you have to wait for all the caching threads to finish before you
unmount.
How do I find out? Is non changing reads/writes enough?
# vmstat -p /dev/sdb4 1
sdb4 reads read sectors writes requested writes
185104 1560696 114662 97396104
185104 1560696 114662 97396104
185104 1560696 114662 97396104
185104 1560696 114662 97396104
--
Tomasz Chmielewski
http://wpkg.org
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