linux-kernel - Re: [PATCH 3/5] KVM: Shrink struct kvm_mmu_memory

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Message-ID: <ddd5d81c-abff-7195-2bf0-039147e3bd80@grsecurity.net>
Date:   Tue, 14 Feb 2023 13:20:07 +0100
From:   Mathias Krause <minipli@...ecurity.net>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 3/5] KVM: Shrink struct kvm_mmu_memory_cache



On 13.02.23 18:08, Sean Christopherson wrote:
> On Mon, Feb 13, 2023, Mathias Krause wrote:
>> Move the 'capacity' member around to make use of the padding hole on 64
>> bit systems instead of introducing yet another one.
>>
>> This allows us to save 8 bytes per instance for 64 bit builds of which,
>> e.g., x86's struct kvm_vcpu_arch has a few.
>>
>> Signed-off-by: Mathias Krause <minipli@...ecurity.net>
>> ---
>>  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 76de36e56cdf..8e4f8fa31457 100644
>> --- a/include/linux/kvm_types.h
>> +++ b/include/linux/kvm_types.h
>> @@ -92,10 +92,10 @@ struct gfn_to_pfn_cache {
>>   */
>>  struct kvm_mmu_memory_cache {
>>  	int nobjs;
>> +	int capacity;
>>  	gfp_t gfp_zero;
>>  	gfp_t gfp_custom;
>>  	struct kmem_cache *kmem_cache;
>> -	int capacity;
>>  	void **objects;
> 
> If we touch this, I vote to do a more aggressive cleanup and place nobjs next
> to objects, e.g.
> 
> struct kvm_mmu_memory_cache {
> 	gfp_t gfp_zero;
> 	gfp_t gfp_custom;
> 	struct kmem_cache *kmem_cache;
> 	int capacity;
> 	int nobjs;
> 	void **objects;
> };

Ok