On 01/18/10 11:17, Carlos R. Mafra wrote:
Hi everyone,
I am using btrfs for my /home partition since I upgraded my slow
laptop hdd for an ssd 3 weeks ago. I am always in sync with Linus'
tree of the day (plus a btrfs patch which is not in there yet) and
so far I haven't lost any data, so all is good.
I have a question about the write behavior of the various [btrfs- ]
kernel threads, as I've been monitoring what is writing to the ssd
just in case.
So what I've been observing with 'iostat', 'iotop' and 'blktrace'
is the following. If my laptop is almost absolutely idle (just
a plain Window Maker and a few xterms and a couple dockapps open)
there is nothing writing to the disk (which is OK).
But as soon as I leave an open tab in chrome (or firefox) the various
[btrfs- ] threads start writing in my /home, and I don't know what.
For testing purposes, I mounted the config dir of chrome (~/.config/google-chrome)
in my SD card (at /dev/mmcblk0p1) to exclude the possibility of maybe chrome
trying to update its history or something, so that it does not write
anything in my /home partition with btrfs.
But I see this in the output of 'iotop' from a 60 sec interval, showing
only the processes which wrote something:
Total DISK READ: 0 B/s | Total DISK WRITE: 10.26 K/s
PID USER DISK READ DISK WRITE SWAPIN IO COMMAND
485 root 0 B/s 5.19 K/s 0.00 % 0.02 % [btrfs-transacti]
3792 root 0 B/s 0 B/s 0.00 % 0.01 % [flush-btrfs-1]
476 root 0 B/s 0.13 K/s 0.00 % 0.00 % [btrfs-delalloc-]
481 root 0 B/s 4.93 K/s 0.00 % 0.00 % [btrfs-endio-wri]
and there are more instances like this. Is there a way to avoid (or reduce)
the writings of these threads?
And when I start opening some pages in chrome and use it some more I
get many many writes on my /home partition from these threads (and swapper,
see below) even though I mounted the .config/google-chrome dir under
/dev/mmcblk0p1 which uses ext4.
From another experiment where chrome was showing a blank tab a ~7 minutes
run of 'blktrace -a write /dev/sda3' (sda3 is my /home) ends like this
(from 'blkparse -s sda3.blktrace.0'):
- snip -
Don't forget cache - should be under ~/.cache/google-chrome. That would
probably explain the disk activity you're seeing.
--Ravi Pinjala
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