On 03/14/2018 02:08 AM, Michal Hocko wrote:
On Mon 05-03-18 13:04:24, Laura Abbott wrote:
On 02/26/2018 06:28 AM, Michal Hocko wrote:
On Fri 23-02-18 11:51:41, Laura Abbott wrote:
Hi,
The Fedora arm-32 build VMs have a somewhat long standing problem
of hanging when running mkfs.ext4 with a bunch of processes stuck
in D state. This has been seen as far back as 4.13 but is still
present on 4.14:
[...]
This looks like everything is blocked on the writeback completing but
the writeback has been throttled. According to the infra team, this problem
is _not_ seen without LPAE (i.e. only 4G of RAM). I did see
https://patchwork.kernel.org/patch/10201593/ but that doesn't seem to
quite match since this seems to be completely stuck. Any suggestions to
narrow the problem down?
How much dirtyable memory does the system have? We do allow only lowmem
to be dirtyable by default on 32b highmem systems. Maybe you have the
lowmem mostly consumed by the kernel memory. Have you tried to enable
highmem_is_dirtyable?
Setting highmem_is_dirtyable did fix the problem. The infrastructure
people seemed satisfied enough with this (and are happy to have the
machines back). I'll see if they are willing to run a few more tests
to get some more state information.
Please be aware that highmem_is_dirtyable is not for free. There are
some code paths which can only allocate from lowmem (e.g. block device
AFAIR) and those could fill up the whole lowmem without any throttling.
Good to note. This particular setup is one basically everyone dislikes
so I think this is only encouragement to move to something else.
Thanks,
Laura
