Re: btrfs-transacti hammering the system

[Andrei Borzenkov <arvidjaar@gmail.com>]

01.12.2017 21:04, Austin S. Hemmelgarn пишет:
> On 2017-12-01 12:13, Andrei Borzenkov wrote:
>> 01.12.2017 20:06, Hans van Kranenburg пишет:
>>>
>>> Additional tips (forgot to ask for your /proc/mounts before):
>>> * Use the noatime mount option, so that only accessing files does not
>>> lead to changes in metadata,
>>
>> Is not 'lazytime" default today?

Sorry, it was relatime that is today's default, I mixed them up.

> It gives you correct atime + no extra
>> metadata update cause by update of atime only.
> Unless things have changed since the last time this came up, BTRFS does
> not support the 'lazytime' mount option (but it doesn't complain about
> it either).
> 

Actually since v2.27 "lazytime" is interpreted by mount command itself
and converted into MS_LAZYTIME flag, so should be available for each FS.

bor@10:~> sudo mkfs -t ext4 /dev/sdb1
mke2fs 1.43.7 (16-Oct-2017)
...

bor@10:~> sudo mount -t ext4 -o lazytime /dev/sdb1 /mnt
bor@10:~> tail /proc/self/mountinfo
...
224 66 8:17 / /mnt rw,relatime shared:152 - ext4 /dev/sdb1
rw,lazytime,data=ordered
bor@10:~> sudo umount /dev/sdb1
bor@10:~> sudo mkfs -t btrfs -f /dev/sdb1
btrfs-progs v4.13.3
...

bor@10:~> sudo mount -t btrfs -o lazytime /dev/sdb1 /mnt
bor@10:~> tail /proc/self/mountinfo
...
224 66 0:88 / /mnt rw,relatime shared:152 - btrfs /dev/sdb1
rw,lazytime,space_cache,subvolid=5,subvol=/
bor@10:~>


> Also, lazytime is independent from noatime, and using both can have
> benefits (lazytime will still have to write out the inode for every file
> read on the system every 24 hours, but with noatime it only has to write
> out the inode for files that have changed).
> 

OK, that's true.