linux-kernel - Re: [PATCH] [1/4] SLAB: Handle node-not-up case in fallback

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Message-ID: <20100206155624.GA2777@one.firstfloor.org>
Date:	Sat, 6 Feb 2010 16:56:24 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andi Kleen <andi@...stfloor.org>, submit@...stfloor.org,
	linux-kernel@...r.kernel.org, haicheng.li@...el.com,
	Pekka Enberg <penberg@...helsinki.fi>, linux-mm@...ck.org
Subject: Re: [PATCH] [1/4] SLAB: Handle node-not-up case in fallback_alloc()

> If a hot-added node has not been initialized for the cache, your code is 
> picking an existing one in zonelist order which may be excluded by 
> current's cpuset.  Thus, your code has a very real chance of having 
> kmem_getpages() return NULL because get_page_from_freelist() will reject 
> non-atomic ALLOC_CPUSET allocations for prohibited nodes.  That isn't a 
> scenario that requires a "funny cpuset," it just has to not allow whatever 
> initialized node comes first in the zonelist.

The point was that you would need to run whoever triggers the memory
hotadd in a cpuset with limitations. That would be a clear
don't do that if hurts(tm)
 
> My suggested alternative does not pick a single initialized node, rather 
> it tries all nodes that actually have a chance of having kmem_getpages() 
> succeed which increases the probability that your patch actually has an 
> effect for cpuset users.

cpuset users are unlikely to trigger memory hotadds from inside limiting
cpusets. Typically that's done from udev etc.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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