Date: Thu, 6 Feb 2014 15:58:17 -0800 (PST)
From: David Rientjes <rientjes@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        Fengguang Wu <fengguang.wu@intel.com>,
        David Cohen <david.a.cohen@linux.intel.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Damien Ramonda <damien.ramonda@intel.com>, Jan Kara <jack@suse.cz>,
        Linus <torvalds@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH V5] mm readahead: Fix readahead fail for no local
 memory and limit readahead pages
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On Thu, 6 Feb 2014, David Rientjes wrote:

> > > > > +#define MAX_REMOTE_READAHEAD   4096UL

> Normally it wouldn't matter because there's no significant downside to it 
> racing, things like mempolicies which use numa_node_id() extensively would 
> result in, oops, a page allocation on the wrong node.
> 
> This stands out to me, though, because you're expecting the calculation to 
> be correct for a specific node.
> 
> The patch is still wrong, though, it should just do
> 
> 	int node = ACCESS_ONCE(numa_mem_id());
> 	return min(nr, (node_page_state(node, NR_INACTIVE_FILE) +
> 		        node_page_state(node, NR_FREE_PAGES)) / 2);
> 
> since we want to readahead based on the cpu's local node, the comment 
> saying we're reading ahead onto "remote memory" is wrong since a 
> memoryless node has local affinity to numa_mem_id().
> 

Oops, forgot about the MAX_REMOTE_READAHEAD which needs to be factored in 
as well, but this handles the bound on local node's statistics.
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