linux-kernel - Re: [patch -mm] cpusets: add memory_slab

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Message-Id: <20090309123011.A228.A69D9226@jp.fujitsu.com>
Date:	Mon,  9 Mar 2009 13:49:27 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Matt Mackall <mpm@...enic.com>,
	Paul Menage <menage@...gle.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch -mm] cpusets: add memory_slab_hardwall flag

> Adds a per-cpuset `memory_slab_hardwall' flag.
> 
> The slab allocator interface for determining whether an object is allowed
> is
> 
> 	int current_cpuset_object_allowed(int node, gfp_t flags)
> 
> This returns non-zero when the object is allowed, either because
> current's cpuset does not have memory_slab_hardwall enabled or because
> it allows allocation on the node.  Otherwise, it returns zero.
> 
> This interface is lockless because a task's cpuset can always be safely
> dereferenced atomically.
> 
> For slab, if the physical node id of the cpu cache is not from an
> allowable node, the allocation will fail.  If an allocation is targeted
> for a node that is not allowed, we allocate from an appropriate one
> instead of failing.
> 
> For slob, if the page from the slob list is not from an allowable node,
> we continue to scan for an appropriate slab.  If none can be used, a new
> slab is allocated.
> 
> For slub, if the cpu slab is not from an allowable node, the partial list
> is scanned for a replacement.  If none can be used, a new slab is
> allocated.

Hmmm,
this description only explay how to implement this.
but no explain why this patch is useful.

Could you please who and why need it?



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