linux-kernel - [patch] mm: Fix incorrect mempolicy for idle threads

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Date:	Mon, 2 Oct 2006 19:49:14 -0700
From:	Ravikiran G Thirumalai <kiran@...lex86.org>
To:	Andrew Morton <akpm@...l.org>
Cc:	linux-kernel@...r.kernel.org,
	Alok Kataria <alok.kataria@...softinc.com>,
	"Shai Fultheim (Shai@...lex86.org)" <shai@...lex86.org>,
	"Benzi Galili (Benzi@...leMP.com)" <benzi@...lemp.com>
Subject: [patch] mm: Fix incorrect mempolicy for idle threads

The kernel boots up on the BP with an initial memory policy of
MPOL_INTERLEAVE (start_kernel() -> numa_policy_init()).  This is
done to avoid all boot data structure allocations to be off the boot
node. Current mainline resets the memory policy to MPOL_DEFAULT at init(), 
just before calling userspace init.  But, this is too late and leaves 
the kernel idle thread with MPOL_INTERLEAVE, causing later allocations 
off interrupt/BH context to use MPOL_INTERLEAVE, rather than MPOL_DEFAULT 
(if the interrupt occurs on an idle cpu).  This can be fixed by changing 
the mempolicy to MPOL_DEFAULT just before the 'init' kernel thread is 
spawned, OR just before smp_init() (smp_init would spawn idle threads).  
The following patch uses the latter approach and moves numa_default_policy() 
to just  before smp_init().

Signed-off-by: Alok N Kataria <alok.kataria@...softinc.com>
Signed-off-by: Ravikiran Thirumalai <kiran@...lex86.org>
Signed-off-by: Shai Fultheim <shai@...lex86.org>

Index: linux-2.6.18/init/main.c
===================================================================
--- linux-2.6.18.orig/init/main.c	2006-09-19 20:42:06.000000000 -0700
+++ linux-2.6.18/init/main.c	2006-09-28 15:13:01.000000000 -0700
@@ -703,6 +703,8 @@ static int init(void * unused)

 	do_pre_smp_initcalls();

+	numa_default_policy();
+
 	smp_init();
 	sched_init_smp();

@@ -738,7 +740,6 @@ static int init(void * unused)
 	unlock_kernel();
 	mark_rodata_ro();
 	system_state = SYSTEM_RUNNING;
-	numa_default_policy();

 	if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
 		printk(KERN_WARNING "Warning: unable to open an initial console.\n");
-
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