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Date: Tue, 30 Jul 2019 00:12:33 +0300 From: Dmitrij Gusev <dmitrij@...ev.co> To: "Theodore Y. Ts'o" <tytso@....edu> Cc: "'linux-ext4@...r.kernel.org'" <linux-ext4@...r.kernel.org> Subject: Re: ext4 file system is constantly writing to the block device with no activity from the applications, is it a bug? Hello. Yes, this is the lazy inode table initialization. After I remounted the FS with a "noinit_itable" option the activity has stopped (then I remounted it back to continue initialization). Appreciate your help. P.S. Thank you, Theodore and the development team involved for the great ext4 filesystem. It is a reliable, high-performance file system. It always served me well for many years and continues to do so. I had never lost any data using it, even though some systems experienced many crashes or power losses. Sincerely, Dmitrij On 2019-07-29 15:55, Theodore Y. Ts'o wrote: > On Mon, Jul 29, 2019 at 02:18:22PM +0300, Dmitrij Gusev wrote: >> A ext4 file system is constantly writing to the block device with no >> activity from the applications, is it a bug? >> >> Write speed is about 64k bytes (almost always exactly 64k bytes) per second >> every 1-2 seconds (I've discovered it after a RAID sync finished). Please >> the check activity log sample below. > Is this a freshly created file system? It could be the lazy inode > table initialization. You can suppress it using "mount -o > noinit_itable", but it will leave portions of the inode table > unzeroed, which can lead to confusion if the system crashes and e2fsck > has to try to recover the file system. > > Or you can not enable lazy inode table initialization when the file > system is created, using "mke2fs -t ext4 -E lazy_itable_init=0 > /dev/XXX". (See the manual page for mke2fs.conf for another way to > turn it off by default.) > > Turning off lazy inode table initialization mke2fs to take **much** > longer, especially on large RAID arrays. The idea is to trade off > mkfs time with background activity to initialize the inode table when > the file system is mounted. The noinit_itable mount option was added > so that a distro installer can temporarily suppress the background > inode table initialization to speed up the install; but then when the > system is booted, it can run in the background later. > > > If that's not it, try installing the blktrace package and then run > "btrace /dev/<vg>/home", and see what it reports. For example, here's > the output from running "touch /mnt/test" (comments prefixed by '#'): > > # here's the touch process reading the inode... > 259,0 2 1 37.115679608 6646 Q RM 4232 + 8 [touch] > 259,0 2 2 37.115682891 6646 C RM 4232 + 8 [0] > # here's the journal commit, 5 seconds later > 259,0 1 11 42.543705759 6570 Q WS 3932216 + 8 [jbd2/pmem0-8] > 259,0 1 12 42.543709184 6570 C WS 3932216 + 8 [0] > 259,0 1 13 42.543713049 6570 Q WS 3932224 + 8 [jbd2/pmem0-8] > 259,0 1 14 42.543714248 6570 C WS 3932224 + 8 [0] > 259,0 1 15 42.543717049 6570 Q WS 3932232 + 8 [jbd2/pmem0-8] > 259,0 1 16 42.543718193 6570 C WS 3932232 + 8 [0] > 259,0 1 17 42.543720895 6570 Q WS 3932240 + 8 [jbd2/pmem0-8] > 259,0 1 18 42.543722028 6570 C WS 3932240 + 8 [0] > 259,0 1 19 42.543724806 6570 Q WS 3932248 + 8 [jbd2/pmem0-8] > 259,0 1 20 42.543725952 6570 C WS 3932248 + 8 [0] > 259,0 1 21 42.543728697 6570 Q WS 3932256 + 8 [jbd2/pmem0-8] > 259,0 1 22 42.543729799 6570 C WS 3932256 + 8 [0] > 259,0 1 23 42.543745380 6570 Q FWFS 3932264 + 8 [jbd2/pmem0-8] > 259,0 1 24 42.543746836 6570 C FWFS 3932264 + 8 [0] > # and here's the writeback to the inode table and superblock, > # 30 seconds later > 259,0 1 25 72.836967205 91 Q W 0 + 8 [kworker/u8:3] > 259,0 1 26 72.836970861 91 C W 0 + 8 [0] > 259,0 1 27 72.836984218 91 Q WM 8 + 8 [kworker/u8:3] > 259,0 1 28 72.836985929 91 C WM 8 + 8 [0] > 259,0 1 29 72.836992108 91 Q WM 4232 + 8 [kworker/u8:3] > 259,0 1 30 72.836993953 91 C WM 4232 + 8 [0] > 259,0 1 31 72.837001370 91 Q WM 4360 + 8 [kworker/u8:3] > 259,0 1 32 72.837003210 91 C WM 4360 + 8 [0] > 259,0 1 33 72.837010993 91 Q WM 69896 + 8 [kworker/u8:3] > 259,0 1 34 72.837012564 91 C WM 69896 + 8 [0] > > Cheers, > > - Ted
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