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Date: Wed, 08 May 2013 02:24:40 +0200
From: "Rafael J. Wysocki" <rjw@...k.pl>
To: Toshi Kani <toshi.kani@...com>
Cc: Vasilis Liaskovitis <vasilis.liaskovitis@...fitbricks.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
isimatu.yasuaki@...fujitsu.com, Len Brown <lenb@...nel.org>,
linux-mm@...ck.org, wency@...fujitsu.com
Subject: Re: [PATCH 2/2 v2, RFC] Driver core: Introduce offline/online callbacks for memory blocks
On Tuesday, May 07, 2013 05:59:16 PM Toshi Kani wrote:
> On Wed, 2013-05-08 at 01:17 +0200, Rafael J. Wysocki wrote:
> > On Tuesday, May 07, 2013 04:45:40 PM Toshi Kani wrote:
> > > On Wed, 2013-05-08 at 00:10 +0200, Rafael J. Wysocki wrote:
> > > > On Tuesday, May 07, 2013 03:03:49 PM Toshi Kani wrote:
> > > > > 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.kani@...com>
> > > >
> > > > OK, one more update, then (appended).
> > > >
> > > > That said I thought that the check against dev->offline in device_offline()
> > > > would be sufficient to guard agaist that. Is there any "offline" code path
> > > > I didn't take into account?
> > >
> > > Oh, you are right about that. The real problem is that dev->offline is
> > > set to false (0) when a new memory is hot-added in off-line state. So,
> > > instead, dev->offline needs to be set properly.
> >
> > OK, where does that happen?
>
> It's a bit messy, but the following change seems to work. A tricky part
> is that online() is not called during boot, so I needed to update the
> offline flag in __memory_block_change_state().
I wonder why? ->
> ---
> drivers/base/memory.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index b9dfd34..1c8d781 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -294,8 +294,10 @@ static int __memory_block_change_state(struct
> memory_block *mem,
> mem->state = from_state_req;
> } else {
> mem->state = to_state;
> - if (to_state == MEM_ONLINE)
> + if (to_state == MEM_ONLINE) {
> mem->last_online = online_type;
> + mem->dev.offline = false;
> + }
->
__memory_block_change_state() is called by memory_subsys_online/offline()
and by __memory_block_change_state_uevent() only, so it should be sufficient
to do this under the switch () in the latter.
Still, though, __memory_block_change_state_uevent() is only called (indirectly)
from store_mem_state() and by offline_memory_block() the both of which update
dev->offline.
What's the exact scenario you needed this for?
> }
> return ret;
> }
> @@ -613,6 +615,7 @@ static int init_memory_block(struct memory_block
> **memory,
> mem->state = state;
> mem->last_online = ONLINE_KEEP;
> mem->section_count++;
> + mem->dev.offline = (state == MEM_OFFLINE) ? true : false;
You could write this as
+ mem->dev.offline = state == MEM_OFFLINE;
Moreover, it'd be better to do it in register_memory(), I think.
> mutex_init(&mem->state_mutex);
> start_pfn = section_nr_to_pfn(mem->start_section_nr);
> mem->phys_device = arch_get_memory_phys_device(start_pfn);
Thanks,
Rafael
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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