Hi, Thank you for your suggestion. It does not help at all. btrfs balance's behaviour seems to be unchanged by ionice. It still takes 100% while working and starves all other processes of disk access.
I can I get btrfs balance to work in the background, without adversely affecting other applications? > > On 23 December 2017 at 11:56, Alberto Bursi <alberto.bu...@outlook.it> wrote: >> >> >> On 12/23/2017 12:19 PM, James Courtier-Dutton wrote: >>> Hi, >>> >>> During a btrfs balance, the process hogs all CPU. >>> Or, to be exact, any other program that wishes to use the SSD during a >>> btrfs balance is blocked for long periods. Long periods being more >>> than 5 seconds. >>> Is there any way to multiplex SSD access while btrfs balance is >>> operating, so that other applications can still access the SSD with >>> relatively low latency? >>> >>> My guess is that btrfs is doing a transaction with a large number of >>> SSD blocks at a time, and thus blocking other applications. >>> >>> This makes for atrocious user interactivity as well as applications >>> failing because they cannot access the disk in a relatively low latent >>> manner. >>> For, example, this is causing a High Definition network CCTV >>> application to fail. >>> >>> What I would really like, is for some way to limit SSD bandwidths to >>> applications. >>> For example the CCTV app always gets the bandwidth it needs, and all >>> other applications can still access the SSD, but are rate limited. >>> This would fix my particular problem. >>> We have rate limiting for network applications, why not disk access also? >>> >>> Kind Regards >>> >>> James >>> >> >> On most I/O intensive programs in Linux you can use "ionice" tool to >> change the disk access priority of a process. [1] >> This allows me to run I/O intensive background scripts in servers >> without the users noticing slowdowns or lagging, of course this means >> the process doing heavy I/O will run more slowly or get outright paused >> if higher-priority processes need a lot of access to the disk. >> >> It works on btrfs balance too, see (commandline example) [2]. >> >> If you don't start the process with ionice as in [2], you can always >> change the priority later if you get the get the process ID. I use iotop >> [3], which also supports commandline arguments to integrate its output >> in scripts. >> >> For btrfs scrub it seems to be possible to specify the ionice options >> directly, while btrfs balance does not seem to have them (would be nice >> to add them imho). [4] >> >> For the sake of completeness, there is also "nice" tool for CPU usage >> priority (also used in my scripts on servers to keep the scripts from >> hogging the CPU for what is just a background process, and seen in [2] >> commandline too). [5] >> >> 1. http://man7.org/linux/man-pages/man1/ionice.1.html >> 2. >> https://unix.stackexchange.com/questions/390480/nice-and-ionice-which-one-should-come-first >> 3. http://man7.org/linux/man-pages/man8/iotop.8.html >> 4. https://btrfs.wiki.kernel.org/index.php/Manpage/btrfs-scrub >> 5. http://man7.org/linux/man-pages/man1/nice.1.html >> >> -Alberto -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
