linux-kernel - Re: [PATCH] memory hotplug: run lru_add_drain

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Date:	Thu, 4 Dec 2008 09:31:43 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	gerald.schaefer@...ibm.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
	y-goto@...fujitsu.com, npiggin@...e.de
Subject: Re: [PATCH] memory hotplug: run lru_add_drain_all() on each cpu

On Wed, 03 Dec 2008 14:16:07 -0800
Dave Hansen <dave@...ux.vnet.ibm.com> wrote:
> > This let us run
> > into the BUG_ON(!PageBuddy(page)) in __offline_isolated_pages() during
> > memory hotplug stress test on s390. The page in question was still on the
> > pcp list, because of a race with lru_add_drain_all() and drain_all_pages()
> > on different cpus.
> > 
> > This is fixed with this patch by adding CONFIG_MEMORY_HOTREMOVE to the
> > lru_add_drain_all() #ifdef, to let it run on each cpu.
> 
> This doesn't seem right to me.  CONFIG_MEMORY_HOTREMOVE doesn't change
> the layout of the LRUs, unlike NUMA or UNEVICTABLE_LRU.  So, I think
> this bug is more due to the hotremove code mis-expecting behavior out of
> lru_add_drain_all().
> 
How about 

#ifdef CONFIG_SMP

#else..

#endif

rather than

-#if defined(CONFIG_NUMA) || defined(CONFIG_UNEVICTABLE_LRU)
+#if defined(CONFIG_NUMA) || defined(CONFIG_UNEVICTABLE_LRU) || \
+    defined(CONFIG_MEMORY_HOTREMOVE)
...

thanks,
-Kame

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