Hello, I'm experiencing periodic write spikes while my system is idle.
According to iotop, they're being caused by "btrfs-endio-write", "btrfs-transaction", and "btrfs-dealloc". Mostly, the issue is with "endio-write": I've seen up to four of these processes write at the same time. Using iostat, I've determined that these writes range from 1 to 6 megabytes in size, and that they occur roughly every 5 seconds. These write spikes may prevent my disk from spinning down and lower my battery life. I fetched the latest unpatched mainline kernel and modified linux/fs/btrfs/inode.c:2051 to add a debugging printk() inside of btrfs_writepage_end_io_hook(). After running that kernel, I can confirm two things; 1. The write spikes occur whenever btrfs does: /* btrfs/inode.c:2051 */ workers = &root->fs_info->endio_write_workers; btrfs_queue_worker(workers, &ordered_extent->work); 2. The write spikes seem to affect only one inode. That is to say, every time there is a write spike, my printk() indicates that it is the exact same inode being written to over and over again. I actually scanned my entire disk for this mysterious inode (using find / -inum ...), and it turned out to be some systemd log in /var/log/journal. I turned off journald and rebooted, but the write spike behavior remained. I tried removing write priviliges to that file and then deleting it outright, but endio-write just picked another inode to write to (which was again in /var/log/journal!). I am not a kernel hacker and I'm not absolutely convinced this is a btrfs issue, but I'd appreciate some pointers in the right direction. best, -vk -- 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
