[PATCH] KVM: Reorder fields in 'struct kvm_mmu_memory_cache'

[PATCH] KVM: Reorder fields in 'struct kvm_mmu_memory_cache'

[Christophe JAILLET]

Group some variables based on their sizes to reduce hole and avoid padding.
On x86_64, this shrinks the size from 40 to 32 bytes.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
Using pahole

Before:
======
struct kvm_mmu_memory_cache {
	int                        nobjs;                /*     0     4 */
	gfp_t                      gfp_zero;             /*     4     4 */
	gfp_t                      gfp_custom;           /*     8     4 */

	/* XXX 4 bytes hole, try to pack */

	struct kmem_cache *        kmem_cache;           /*    16     8 */
	int                        capacity;             /*    24     4 */

	/* XXX 4 bytes hole, try to pack */

	void * *                   objects;              /*    32     8 */

	/* size: 40, cachelines: 1, members: 6 */
	/* sum members: 32, holes: 2, sum holes: 8 */
	/* last cacheline: 40 bytes */
};
---
 include/linux/kvm_types.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
index 2728d49bbdf6..76af8425dbc6 100644
--- a/include/linux/kvm_types.h
+++ b/include/linux/kvm_types.h
@@ -94,8 +94,8 @@ struct kvm_mmu_memory_cache {
 	int nobjs;
 	gfp_t gfp_zero;
 	gfp_t gfp_custom;
-	struct kmem_cache *kmem_cache;
 	int capacity;
+	struct kmem_cache *kmem_cache;
 	void **objects;
 };
 #endif
-- 
2.34.1

Re: [PATCH] KVM: Reorder fields in 'struct kvm_mmu_memory_cache'

[Sean Christopherson]

On Fri, Feb 17, 2023, Christophe JAILLET wrote:
> Group some variables based on their sizes to reduce hole and avoid padding.
> On x86_64, this shrinks the size from 40 to 32 bytes.

Heh, a hair too late[*].  Unless I'm mistaken, Mathias will be sending a new
version in the not-too-distant future.

Thanks!

[*] https://lore.kernel.org/all/Y+puefrgtqf430fs@google.com

Re: [PATCH] KVM: Reorder fields in 'struct kvm_mmu_memory_cache'

[Christophe JAILLET]

Le 17/02/2023 à 17:41, Sean Christopherson a écrit :
> On Fri, Feb 17, 2023, Christophe JAILLET wrote:
>> Group some variables based on their sizes to reduce hole and avoid padding.
>> On x86_64, this shrinks the size from 40 to 32 bytes.
> 
> Heh, a hair too late[*].  Unless I'm mistaken, Mathias will be sending a new
> version in the not-too-distant future.
> 
> Thanks!
> 
> [*] https://lore.kernel.org/all/Y+puefrgtqf430fs@google.com
> 

Ok, great :)

Thanks for the feed-back.

CJ

Re: [PATCH] KVM: Reorder fields in 'struct kvm_mmu_memory_cache'

[Mathias Krause]

On 17.02.23 17:41, Sean Christopherson wrote:
> On Fri, Feb 17, 2023, Christophe JAILLET wrote:
>> Group some variables based on their sizes to reduce hole and avoid padding.
>> On x86_64, this shrinks the size from 40 to 32 bytes.
> 
> Heh, a hair too late[*].  Unless I'm mistaken, Mathias will be sending a new
> version in the not-too-distant future.

Jepp, patches should appear here anytime soon:

https://lore.kernel.org/kvm/20230217193336.15278-1-minipli@grsecurity.net

> 
> Thanks!
> 
> [*] https://lore.kernel.org/all/Y+puefrgtqf430fs@google.com