slub: Do not use 192 byte sized cache if minimum alignment is 128 byte

slub: Do not use 192 byte sized cache if minimum alignment is 128 byte

[Christoph Lameter]

The 192 byte cache is not necessary if we have a basic alignment of 128
byte. If it would be used then the 192 would be aligned to the next 128 byte
boundary which would result in another 256 byte cache. Two 256 kmalloc caches
cause sysfs to complain about a duplicate entry.

MIPS needs 128 byte aligned kmalloc caches and spits out warnings on boot without
this patch.

Signed-off-by: Christoph Lameter <cl@linux-foundation.org>

Index: linux-2.6/include/linux/slub_def.h
===================================================================
--- linux-2.6.orig/include/linux/slub_def.h	2008-07-02 13:57:29.000000000 -0500
+++ linux-2.6/include/linux/slub_def.h	2008-07-02 13:58:00.000000000 -0500
@@ -137,10 +137,12 @@
 	if (size <= KMALLOC_MIN_SIZE)
 		return KMALLOC_SHIFT_LOW;
 
+#if KMALLOC_MIN_SIZE <= 64
 	if (size > 64 && size <= 96)
 		return 1;
 	if (size > 128 && size <= 192)
 		return 2;
+#endif
 	if (size <=          8) return 3;
 	if (size <=         16) return 4;
 	if (size <=         32) return 5;
Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2008-07-02 13:57:29.000000000 -0500
+++ linux-2.6/mm/slub.c	2008-07-02 13:58:07.000000000 -0500
@@ -2995,8 +2995,6 @@
 		create_kmalloc_cache(&kmalloc_caches[1],
 				"kmalloc-96", 96, GFP_KERNEL);
 		caches++;
-	}
-	if (KMALLOC_MIN_SIZE <= 128) {
 		create_kmalloc_cache(&kmalloc_caches[2],
 				"kmalloc-192", 192, GFP_KERNEL);
 		caches++;
@@ -3026,6 +3024,16 @@
 	for (i = 8; i < KMALLOC_MIN_SIZE; i += 8)
 		size_index[(i - 1) / 8] = KMALLOC_SHIFT_LOW;
 
+	if (KMALLOC_MIN_SIZE == 128) {
+		/*
+		 * The 192 byte sized cache is not used if the alignment
+		 * is 128 byte. Redirect kmalloc to use the 256 byte cache
+		 * instead.
+		 */
+		for (i = 128 + 8; i <= 192; i += 8)
+			size_index[(i - 1) / 8] = 8;
+	}
+
 	slab_state = UP;
 
 	/* Provide the correct kmalloc names now that the caches are up */

Re: slub: Do not use 192 byte sized cache if minimum alignment is 128 byte

[Pekka Enberg]

On Thu, Jul 3, 2008 at 5:14 PM, Christoph Lameter
<cl@linux-foundation.org> wrote:
> The 192 byte cache is not necessary if we have a basic alignment of 128
> byte. If it would be used then the 192 would be aligned to the next 128 byte
> boundary which would result in another 256 byte cache. Two 256 kmalloc caches
> cause sysfs to complain about a duplicate entry.
>
> MIPS needs 128 byte aligned kmalloc caches and spits out warnings on boot without
> this patch.
>
> Signed-off-by: Christoph Lameter <cl@linux-foundation.org>

Looks good to me. Yoichi, did you have the chance to test this?
Christoph, are the warnings harmless or do we need to get this into
2.6.26?

Re: slub: Do not use 192 byte sized cache if minimum alignment is 128 byte

[Christoph Lameter]

I think this needs to go into .26.

Re: slub: Do not use 192 byte sized cache if minimum alignment is 128 byte

[Yoichi Yuasa]

On Thu, 3 Jul 2008 18:37:52 +0300
"Pekka Enberg" <penberg@cs.helsinki.fi> wrote:

> On Thu, Jul 3, 2008 at 5:14 PM, Christoph Lameter
> <cl@linux-foundation.org> wrote:
> > The 192 byte cache is not necessary if we have a basic alignment of 128
> > byte. If it would be used then the 192 would be aligned to the next 128 byte
> > boundary which would result in another 256 byte cache. Two 256 kmalloc caches
> > cause sysfs to complain about a duplicate entry.
> >
> > MIPS needs 128 byte aligned kmalloc caches and spits out warnings on boot without
> > this patch.
> >
> > Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
> 
> Looks good to me. Yoichi, did you have the chance to test this?

I've already done.
It has no problem.

Yoichi

Re: slub: Do not use 192 byte sized cache if minimum alignment is 128 byte

[Pekka Enberg]

Hi Yoichi,

On Thu, Jul 3, 2008 at 5:14 PM, Christoph Lameter
<cl@linux-foundation.org> wrote:
>>> The 192 byte cache is not necessary if we have a basic alignment of 128
>>> byte. If it would be used then the 192 would be aligned to the next 128 byte
>>> boundary which would result in another 256 byte cache. Two 256 kmalloc caches
>>> cause sysfs to complain about a duplicate entry.
>>>
>>> MIPS needs 128 byte aligned kmalloc caches and spits out warnings on boot without
>>> this patch.
>>>
>>> Signed-off-by: Christoph Lameter <cl@linux-foundation.org>

On Thu, 3 Jul 2008 18:37:52 +0300
"Pekka Enberg" <penberg@cs.helsinki.fi> wrote:
>> Looks good to me. Yoichi, did you have the chance to test this?

On Fri, Jul 4, 2008 at 3:28 AM, Yoichi Yuasa
<yoichi_yuasa@tripeaks.co.jp> wrote:
> I've already done.
> It has no problem.

Thank you for testing!