On Tue, 2013-05-07 at 14:11 +0200, Rafael J. Wysocki wrote:
> On Tuesday, May 07, 2013 12:59:45 PM Vasilis Liaskovitis wrote:
:
> Updated patch is appended for completness.
Yes, this updated patch solved the locking issue.
> > > > A more general issue is that there are now two memory offlining efforts:
> > > >
> > > > 1) from acpi_bus_offline_companions during device offline
> > > > 2) from mm: remove_memory during device detach (offline_memory_block_cb)
> > > >
> > > > The 2nd is only called if the device offline operation was already
> > > > succesful, so
> > > > it seems ineffective or redundant now, at least for
> > > > x86_64/acpi_memhotplug machine
> > > > (unless the blocks were re-onlined in between).
> > >
> > > Sure, and that should be OK for now. Changing the detach behavior is not
> > > essential from the patch [2/2] perspective, we can do it later.
> >
> > yes, ok.
> >
> > >
> > > > On the other hand, the 2nd effort has some more intelligence in
> > > > offlining, as it
> > > > tries to offline twice in the precense of memcg, see commits df3e1b91 or
> > > > reworked 0baeab16. Maybe we need to consolidate the logic.
> > >
> > > Hmm. Perhaps it would make sense to implement that logic in
> > > memory_subsys_offline(), then?
> >
> > the logic tries to offline the memory blocks of the device twice, because
> > the
> > first memory block might be storing information for the subsequent
> > memblocks.
> >
> > memory_subsys_offline operates on one memory block at a time. Perhaps we
> > can get
> > the same effect if we do an acpi_walk of acpi_bus_offline_companions twice
> > in
> > acpi_scan_hot_remove but it's probably not a good idea, since that would
> > affect non-memory devices as well.
> >
> > I am not sure how important this intelligence is in practice (I am not using
> > mem cgroups in my guest kernel tests yet). Maybe Wen (original author) has
> > more details on 2-pass offlining effectiveness.
>
> OK
>
> It may be added in a separate patch in any case.
I had the same comment as Vasilis. And, I agree with you that we can
enhance it in separate patches.
:
> +static int memory_subsys_offline(struct device *dev)
> +{
> + struct memory_block *mem = container_of(dev, struct memory_block, dev);
> + int ret;
> +
> + mutex_lock(&mem->state_mutex);
> + ret = __memory_block_change_state(mem, MEM_OFFLINE, MEM_ONLINE, -1);
This function needs to check mem->state just like
offline_memory_block(). That is:
int ret = 0;
:
if (mem->state != MEM_OFFLINE)
ret = __memory_block_change_state(...);
Otherwise, memory hot-delete to an off-lined memory fails in
__memory_block_change_state() since mem->state is already set to
MEM_OFFLINE.
With that change, for the series:
Reviewed-by: Toshi Kani <toshi.k...@hp.com>
Thanks,
-Toshi
> + mutex_unlock(&mem->state_mutex);
> + return ret;
> +}
> +
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