Brian Foster wrote:

On Fri, Feb 03, 2017 at 03:50:09PM +0100, Michal Hocko wrote:

quoted

[Let's CC more xfs people]

On Fri 03-02-17 19:57:39, Tetsuo Handa wrote:
[...]

quoted

(1) I got an assertion failure.

I suspect this is a result of
http://lkml.kernel.org/r/20170201092706.9966-2-mhocko@kernel.org
I have no idea what the assert means though.

quoted

[  969.626518] Killed process 6262 (oom-write) total-vm:2166856kB, anon-rss:1128732kB, file-rss:4kB, shmem-rss:0kB
[  969.958307] oom_reaper: reaped process 6262 (oom-write), now anon-rss:0kB, file-rss:0kB, shmem-rss:0kB
[  972.114644] XFS: Assertion failed: oldlen > newlen, file: fs/xfs/libxfs/xfs_bmap.c, line: 2867

Indirect block reservation underrun on delayed allocation extent merge.
These are extra blocks are used for the inode bmap btree when a delalloc
extent is converted to physical blocks. We're in a case where we expect
to only ever free excess blocks due to a merge of extents with
independent reservations, but a situation occurs where we actually need
blocks and hence the assert fails. This can occur if an extent is merged
with one that has a reservation less than the expected worst case
reservation for its size (due to previous extent splits due to hole
punches, for example). Therefore, I think the core expectation that
xfs_bmap_add_extent_hole_delay() will always have enough blocks
pre-reserved is invalid.

Can you describe the workload that reproduces this? FWIW, I think the
way xfs_bmap_add_extent_hole_delay() currently works is likely broken
and have a couple patches to fix up indlen reservation that I haven't
posted yet. The diff that deals with this particular bit is appended.
Care to give that a try?

The workload is to write to a single file on XFS from 10 processes demonstrated at
http://lkml.kernel.org/r/201512052133.IAE00551.LSOQFtMFFVOHOJ@I-love.SAKURA.ne.jp
using "while :; do ./oom-write; done" loop on a VM with 4CPUs / 2048MB RAM.
With this XFS_FILBLKS_MIN() change applied, I no longer hit assertion failures.

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