Re: Update: [Automatic] NUMA replicated pagecache on 2.6.23-rc4-mm1

[Balbir Singh <balbir@linux.vnet.ibm.com>]

Lee Schermerhorn wrote:
> [Balbir:  see notes re:  replication and memory controller below]
> 
> A quick update:  I have rebased the automatic/lazy page migration and
> replication patches to 23-rc4-mm1.  If interested, you can find the
> entire series that I push in the '070911' tarball at:
> 
> 	http://free.linux.hp.com/~lts/Patches/Replication/
> 
> I haven't gotten around to some of the things you suggested to address
> the soft lockups. etc.  I just wanted to keep the patches up to date.  
> 
> In the process of doing a quick sanity test, I encountered an issue with
> replication and the new memory controller patches.  I had built the
> kernel with the memory controller enabled.  I encountered a panic in
> reclaim, while attempting to "drop caches", because replication was not
> "charging" the replicated pages and reclaim tried to deref a null
> "page_container" pointer.  [!!! new member in page struct !!!]
> 
> I added code to try_to_create_replica(), __remove_replicated_page() and
> release_pcache_desc() to charge/uncharge where I thought appropriate
> [replication patch # 02].  That seemed to solve the panic during drop
> caches triggered reclaim.  However, when I tried a more stressful load,
> I hit another panic ["NaT Consumption" == ia64-ese for invalid pointer
> deref, I think] in shrink_active_list() called from direct reclaim.
> Still to be investigated.  I wanted to give you and Balbir a heads up
> about the interaction of memory controllers with page replication.
> 

Hi, Lee,

Thanks for testing the memory controller with page replication. I do
have some questions on the problem you are seeing

Did you see the problem with direct reclaim or container reclaim?
drop_caches calls remove_mapping(), which should eventually call
the uncharge routine. We have some sanity checks in there.

We do try to see at several places if the page->page_container is NULL
and check for it. I'll look at your patches to see if there are any
changes to the reclaim logic. I tried looking for the oops you
mentioned, but could not find it in your directory, I saw the soft
lockup logs though. Do you still have the oops saved somewhere?

I think the fix you have is correct and makes things works, but it
worries me that in direct reclaim we dereference the page_container
pointer without the page belonging to a container? What are the
properties of replicated pages? Are they assumed to be exact
replicas (struct page mappings, page_container expected to be the
same for all replicated pages) of the replicated page?


> Later,
> Lee
> 
-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>