linux-kernel - Re: [PATCH] mm: create a separate slab for page->ptl allocation

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Date:	Wed, 6 Nov 2013 12:18:45 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH] mm: create a separate slab for page->ptl allocation

On Wed, Nov 06, 2013 at 10:31:31AM +0100, Peter Zijlstra wrote:
> Subject: mm: Properly separate the bloated ptl from the regular case
> 
> Use kernel/bounds.c to convert build-time spinlock_t size into a
> preprocessor symbol and apply that to properly separate the page::ptl
> situation.
> 
> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> ---
>  include/linux/mm.h       | 24 +++++++++++++-----------
>  include/linux/mm_types.h |  9 +++++----
>  kernel/bounds.c          |  2 ++
>  mm/memory.c              | 11 +++++------
>  4 files changed, 25 insertions(+), 21 deletions(-)
> 
> diff --git a/kernel/bounds.c b/kernel/bounds.c
> index e8ca97b5c386..5982437eca2c 100644
> --- a/kernel/bounds.c
> +++ b/kernel/bounds.c
> @@ -11,6 +11,7 @@
>  #include <linux/kbuild.h>
>  #include <linux/page_cgroup.h>
>  #include <linux/log2.h>
> +#include <linux/spinlock.h>
>  
>  void foo(void)
>  {
> @@ -21,5 +22,6 @@ void foo(void)
>  #ifdef CONFIG_SMP
>  	DEFINE(NR_CPUS_BITS, ilog2(CONFIG_NR_CPUS));
>  #endif
> +	DEFINE(BLOATED_SPINLOCKS, sizeof(spinlock_t) > sizeof(int));
>  	/* End of constants */
>  }

Using that we could also do.. not been near a compiler.

---
Subject: lockref: Use bloated_spinlocks to avoid explicit config dependencies

Avoid the fragile Kconfig construct guestimating spinlock_t sizes; use a
friendly compile-time test to determine this.

Not-Signed-off-by: Peter Zijlstra <peterz@...radead.org>
---
 lib/Kconfig   | 3 ---
 lib/lockref.c | 2 +-
 2 files changed, 1 insertion(+), 4 deletions(-)

diff --git a/lib/Kconfig b/lib/Kconfig
index b3c8be0da17f..254af289d1d0 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -54,9 +54,6 @@ config ARCH_USE_CMPXCHG_LOCKREF
 config CMPXCHG_LOCKREF
 	def_bool y if ARCH_USE_CMPXCHG_LOCKREF
 	depends on SMP
-	depends on !GENERIC_LOCKBREAK
-	depends on !DEBUG_SPINLOCK
-	depends on !DEBUG_LOCK_ALLOC
 
 config CRC_CCITT
 	tristate "CRC-CCITT functions"
diff --git a/lib/lockref.c b/lib/lockref.c
index 6f9d434c1521..a158fd86aa1a 100644
--- a/lib/lockref.c
+++ b/lib/lockref.c
@@ -1,7 +1,7 @@
 #include <linux/export.h>
 #include <linux/lockref.h>
 
-#ifdef CONFIG_CMPXCHG_LOCKREF
+#if defined(CONFIG_CMPXCHG_LOCKREF) && !BLOATED_SPINLOCKS
 
 /*
  * Allow weakly-ordered memory architectures to provide barrier-less
--
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