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Date: Wed, 07 Apr 2010 19:29:56 +0300
From: Pekka Enberg <penberg@cs.helsinki.fi>
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To: David Rientjes <rientjes@google.com>
CC: Nick Piggin <npiggin@suse.de>, Andi Kleen <andi@firstfloor.org>,
       Christoph Lameter <cl@linux-foundation.org>,
       linux-kernel@vger.kernel.org, linux-mm@kvack.org, haicheng.li@intel.com,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: [patch v2] slab: add memory hotplug support
References: <alpine.DEB.2.00.1002242357450.26099@chino.kir.corp.google.com> <alpine.DEB.2.00.1002251228140.18861@router.home> <20100226114136.GA16335@basil.fritz.box> <alpine.DEB.2.00.1002260904311.6641@router.home> <20100226155755.GE16335@basil.fritz.box> <alpine.DEB.2.00.1002261123520.7719@router.home> <alpine.DEB.2.00.1002261555030.32111@chino.kir.corp.google.com> <alpine.DEB.2.00.1003010224170.26824@chino.kir.corp.google.com> <20100305062002.GV8653@laptop> <alpine.DEB.2.00.1003081502400.30456@chino.kir.corp.google.com> <20100309134633.GM8653@laptop> <alpine.DEB.2.00.1003271849260.7249@chino.kir.corp.google.com> <alpine.DEB.2.00.1003271940190.8399@chino.kir.corp.google.com>
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David Rientjes wrote:
> Slab lacks any memory hotplug support for nodes that are hotplugged
> without cpus being hotplugged.  This is possible at least on x86
> CONFIG_MEMORY_HOTPLUG_SPARSE kernels where SRAT entries are marked
> ACPI_SRAT_MEM_HOT_PLUGGABLE and the regions of RAM represent a seperate
> node.  It can also be done manually by writing the start address to
> /sys/devices/system/memory/probe for kernels that have
> CONFIG_ARCH_MEMORY_PROBE set, which is how this patch was tested, and
> then onlining the new memory region.
> 
> When a node is hotadded, a nodelist for that node is allocated and 
> initialized for each slab cache.  If this isn't completed due to a lack
> of memory, the hotadd is aborted: we have a reasonable expectation that
> kmalloc_node(nid) will work for all caches if nid is online and memory is
> available.  
> 
> Since nodelists must be allocated and initialized prior to the new node's
> memory actually being online, the struct kmem_list3 is allocated off-node
> due to kmalloc_node()'s fallback.
> 
> When an entire node would be offlined, its nodelists are subsequently
> drained.  If slab objects still exist and cannot be freed, the offline is
> aborted.  It is possible that objects will be allocated between this
> drain and page isolation, so it's still possible that the offline will
> still fail, however.
> 
> Signed-off-by: David Rientjes <rientjes@google.com>

I queued this up for 2.6.35. Thanks!