From: "Марк Коренберг" <socketpair@gmail.com>
To: linux-btrfs@vger.kernel.org
Subject: Major bug in BTRFS (syncs are ignored with libaio or io_uring)
Date: Fri, 28 Oct 2022 00:21:04 +0300 [thread overview]
Message-ID: <CAEmTpZGRKbzc16fWPvxbr6AfFsQoLmz-Lcg-7OgJOZDboJ+SGQ@mail.gmail.com> (raw)
How to reproduce (I tested in kernel 6.1):
2. mkfs.btrfs over a partition.
3. mount -o lazytime,noatime
4. touch file.dat
5. chattr +C file.dat # turns off compression, checksumming and COW
6. fallocate -l1G file.dat
7. # prefill the file with random data
fio -ioengine=psync -name=test -bs=1M
-rw=write -filename=file.dat
8. fio -ioengine=psync -sync=1 -direct=1 -name=test -bs=4k
-rw=randwrite -runtime=60 -filename=file.dat # Will show, say, 2K
IOPs
9. fio -ioengine=io_uring -sync=1 -direct=1 -name=test -bs=4k
-rw=randwrite -runtime=60 -filename=file.dat # Will show, say, 32K
IOPs
10. fio -ioengine=libaio -sync=1 -direct=1 -name=test -bs=4k
-rw=randwrite -runtime=60 -filename=file.dat # Will show, say, 32K
IOPs
Steps 9 and 10 show implausible IOPs.
This does not happen on, say, Ext4 (all the methods give roughly the same IOPs).
Removing -sync=1 on all engines on Ext4 gives immediate return (as
expected because everything gets merged and finally written very fast)
Adding/Removing -sync=1 with io_uring or libaio changes nothing on
BTRFS (it's definitely a bug)
I consider it's a bug in BTRFS. Very important bug because BTRFS
becomes default FS in Fedora server/desktop now. This bug may cause
data loss. That's why I set this bug as high priority.
*****************
https://bugzilla.redhat.com/show_bug.cgi?id=2117971
*****************
--
Segmentation fault
next reply other threads:[~2022-10-27 21:21 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-27 21:21 Марк Коренберг [this message]
2022-10-28 4:30 ` Major bug in BTRFS (syncs are ignored with libaio or io_uring) Andrei Borzenkov
2022-10-28 4:48 ` Марк Коренберг
2022-10-28 10:23 ` Filipe Manana
2022-11-11 12:01 ` Filipe Manana
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