From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ravi Pinjala Subject: Re: btrfs write behavior on idle system Date: Mon, 18 Jan 2010 12:14:43 -0600 Message-ID: <4B54A513.7060902@p-static.net> References: <20100118171756.GA4165@Pilar.aei.mpg.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: linux-btrfs@vger.kernel.org To: "Carlos R. Mafra" Return-path: In-Reply-To: <20100118171756.GA4165@Pilar.aei.mpg.de> List-ID: 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