Hi, Dennis Zhou, Vlastimil Babka, Filipe Manana
The root reason of this problem maybe the design of
'memalloc_nofs_restore()/memalloc_nofs_save()'.
When some job such as memory pre-alloc and reclaim is needed, that is
done in a workqueue now.
This is a problem for high-load and over-load. In that case, we need to
do these job in current task/process, so that current task/process will
be blocked until necessary job is done.
If we let these job in done in a workqueue, and current task/process is
not blocked, that means failure is very near, and then we can not work
stable in high-load and over-load.
For high-load and over-load, failure is not expected, we expect some
job be blocked well.
> > Percpu does do this via a workqueue item. The issue is in v5.9 we
> > introduced 2 types of chunks. However, the free float page number was
> > for the total. So even if 1 chunk type dropped below, the other chunk
> > type might have enough pages. I'm queuing this for 5.12 and will send it
> > out assuming it does fix your problem.
Best Regards
Wang Yugui (wangyugui@xxxxxxxxxxxx)
2021/04/09
> +CC btrfs
>
> On 4/1/21 12:51 PM, Wang Yugui wrote:
> > Hi,
> >
> > an unexpected -ENOMEM from percpu_counter_init() happened when xfstest
> > with kernel 5.11.10 and 5.10.27
>
> Is there a dmesg log showing allocation failure or something?
>
> > direct caller:
> > int btrfs_drew_lock_init(struct btrfs_drew_lock *lock)
> > {
> > int ret;
> >
> > ret = percpu_counter_init(&lock->writers, 0, GFP_KERNEL);
> > if (ret)
> > return ret;
> >
> > atomic_set(&lock->readers, 0);
> > init_waitqueue_head(&lock->pending_readers);
> > init_waitqueue_head(&lock->pending_writers);
> >
> > return 0;
> > }
> >
> > upper caller:
> > nofs_flag = memalloc_nofs_save();
> > ret = btrfs_drew_lock_init(&root->snapshot_lock);
> > memalloc_nofs_restore(nofs_flag);
> > if (ret == -ENOMEM) printk("ENOMEM btrfs_drew_lock_init\n");
> > if (ret)
> > goto fail;
> >
> > The hardware of this server:
> > CPU: Xeon(R) CPU E5-2660 v2(10 core) *2
> > memory: 192G, no swap
> >
> > Only one xfstests job is running in this server, and about 7% of memory
> > is used.
> >
> > Any advice please.
> >
> > Best Regards
> > Wang Yugui (wangyugui@xxxxxxxxxxxx)
> > 2021/04/01
> >
> >
