On Wed 05-04-17 10:48:52, Reza Arbab wrote:
> On Wed, Apr 05, 2017 at 08:42:39AM +0200, Michal Hocko wrote:
> >On Tue 04-04-17 16:43:39, Reza Arbab wrote:
> >>Okay, getting further. With this I can again repeatedly add and remove,
> >>but now I'm seeing a weird variation of that earlier issue:
> >>
> >>1. add_memory(), online_movable
> >> /sys/devices/system/node/nodeX/memoryY symlinks are created.
> >>
> >>2. offline, remove_memory()
> >> The node is offlined, since all memory has been removed, so all of
> >> /sys/devices/system/node/nodeX is gone. This is normal.
> >>
> >>3. add_memory(), online_movable
> >> The node is onlined, so /sys/devices/system/node/nodeX is recreated,
> >> and the memory is added, but just like earlier in this email thread,
> >> the memoryY links are not there.
> >
> >Could you add some printks to see why the sysfs creation failed please?
>
> Ah, simple enough. It's this, right at the top of
> register_mem_sect_under_node():
>
> if (!node_online(nid))
> return 0;
>
> That being the case, I really don't understand why your patches make any
> difference. Is node_set_online() being called later than before somehow?
This is really interesting. Because add_memory_resource does the
following
/* call arch's memory hotadd */
ret = arch_add_memory(nid, start, size);
if (ret < 0)
goto error;
/* we online node here. we can't roll back from here. */
node_set_online(nid);
so we are setting the node online _after_ arch_add_memory but the code
which adds those sysfs file is called from
arch_add_memory
__add_pages
__add_section
register_new_memory
register_mem_sect_under_node
node_online check
I haven't touched this part. What is the point of this check anyway? We
have already associated all the pages with a node (and with a zone prior
to my patches) so we _know_ how to create those links. The check goes
back to the initial submissions. Gary is not available anymore so we
cannot ask. But I completely fail to see how my changes could have made
any difference.
I assume that things start working after you remove that check? Btw. if
you put printk to the original kernel does it see the node online? I
would be also interested whether you see try_offline_node setting the
node offline in the original code.
Thanks!
--
Michal Hocko
SUSE Labs
