Re: Hangs in balance_dirty_pages with arm-32 LPAE + highmem

[Laura Abbott <labbott@redhat.com>]

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.

Thanks,
Laura

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