[RFC]mm/zsmalloc,: trigger BUG_ON in function zs_map_object.

[Yisheng Xie]

Hi, all,

We had backport the no-lru migration to linux-4.1, meanwhile change the
ZS_MAX_ZSPAGE_ORDER to 3. Then we met a BUG_ON(!page[1]).

It rarely happen, and presently, what I get is:
[6823.316528s]obj=a160701f, obj_idx=15, class{size:2176,objs_per_zspage:15,pages_per_zspage:8}
[...]
[6823.316619s]BUG: failure at /home/ethan/kernel/linux-4.1/mm/zsmalloc.c:1458/zs_map_object()! ----> BUG_ON(!page[1])

It seems that we have allocated an object from a ZS_FULL group?
(Actuallyï I do not get the inuse number of this zspage, which I am trying to.)
And presently, I can not find why it happened. Any idea about it?

Any comment is more than welcome!

Thanks
Yisheng Xie