linux-kernel - [PATCH] x86/mm/fault: Put pgd

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Date:	Wed, 10 Jun 2015 09:08:28 -0400
From:	Waiman Long <Waiman.Long@...com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Cc:	linux-kernel@...r.kernel.org, Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>,
	Waiman Long <Waiman.Long@...com>
Subject: [PATCH] x86/mm/fault: Put pgd_lock in its own cacheline

On a large system with many cores, massive creation or destruction
of processes/threads can sometime cause a fair amount of spinlock
contention in the pgd_lock used by the pgd_alloc() and pgd_free()
functions. This patch tries to reduce false cacheline sharing by
putting the pgd_lock in its own cacheline which help to reduce
contention on the lock.

Signed-off-by: Waiman Long <Waiman.Long@...com>
---
 arch/x86/mm/fault.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 181c53b..fae48df 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -185,7 +185,7 @@ force_sig_info_fault(int si_signo, int si_code, unsigned long address,
 	force_sig_info(si_signo, &info, tsk);
 }
 
-DEFINE_SPINLOCK(pgd_lock);
+__cacheline_aligned_in_smp DEFINE_SPINLOCK(pgd_lock);
 LIST_HEAD(pgd_list);
 
 #ifdef CONFIG_X86_32
-- 
1.7.1

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