linux-kernel - Re: vmalloced stacks on x86

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Date:	Sun, 26 Oct 2014 09:46:04 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andy Lutomirski <luto@...capital.net>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: vmalloced stacks on x86_64?

On Fri, 2014-10-24 at 19:38 -0700, H. Peter Anvin wrote:
> On 10/24/2014 05:22 PM, Andy Lutomirski wrote:
> > Is there any good reason not to use vmalloc for x86_64 stacks?
> 
> Additional TLB pressure if anything else.

It seems TLB pressure gets less and less interest these days...

Is it still worth trying to reduce it ?

I was wondering for example why 'hashdist' is not cleared if current
host runs a NUMA enabled kernel, but has a single node.

Something like following maybe ?

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 7dbe5ec9d9cd08afac13797e2adac291fb703eec..0846ef054b0620a7be0c6f69b1a2f21c78d57d3b 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1181,7 +1181,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 	hashdist=	[KNL,NUMA] Large hashes allocated during boot
 			are distributed across NUMA nodes.  Defaults on
 			for 64-bit NUMA, off otherwise.
-			Format: 0 | 1 (for off | on)
+			Format: 0 | 1 | 2 (for off | on if NUMA host | on)
 
 	hcl=		[IA-64] SGI's Hardware Graph compatibility layer
 
diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
index 1a883705a12a8a12410914be93b2ee65807cc423..8aded4c11c8c1cc5778e9ae2b9cd5146070b5b03 100644
--- a/arch/x86/mm/numa.c
+++ b/arch/x86/mm/numa.c
@@ -668,7 +668,8 @@ static int __init dummy_numa_init(void)
 
 	node_set(0, numa_nodes_parsed);
 	numa_add_memblk(0, 0, PFN_PHYS(max_pfn));
-
+	if (hashdist == HASHDIST_DEFAULT)
+		hashdist = 0;
 	return 0;
 }
 


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