linux-kernel - Re: [PATCH v2 5/6] KVM: sort memslots by its size and use line search

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Message-ID: <4EC9C9FF.6020503@linux.vnet.ibm.com>
Date:	Mon, 21 Nov 2011 11:48:15 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 5/6] KVM: sort memslots by its size and use line search

On 11/20/2011 07:26 PM, Avi Kivity wrote:

> On 11/18/2011 11:19 AM, Xiao Guangrong wrote:
>> Sort memslots base on its size and use line search to find it, so the larger
>> memslots have better fit
>>
>> The idea is from Avi
>>
>> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
>> ---
>>  include/linux/kvm_host.h |   22 +++++++++---
>>  virt/kvm/kvm_main.c      |   82 ++++++++++++++++++++++++++++++++-------------
>>  2 files changed, 75 insertions(+), 29 deletions(-)
>>
>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
>> index a0e4d63..83b396a 100644
>> --- a/include/linux/kvm_host.h
>> +++ b/include/linux/kvm_host.h
>> @@ -230,8 +230,12 @@ struct kvm_irq_routing_table {};
>>  #define KVM_MEM_SLOTS_NUM (KVM_MEMORY_SLOTS + KVM_PRIVATE_MEM_SLOTS)
>>  #endif
>>
>> +/*
>> + * Note:
>> + * memslots are not sorted by id anymore, please use id_to_memslot()
>> + * to get the memslot by its id.
>> + */
>>  struct kvm_memslots {
>> -	int nmemslots;
>>  	u64 generation;
>>  	struct kvm_memory_slot memslots[KVM_MEM_SLOTS_NUM];
>>  };
>> @@ -307,9 +311,10 @@ static inline struct kvm_vcpu *kvm_get_vcpu(struct kvm *kvm, int i)
>>  	     (vcpup = kvm_get_vcpu(kvm, idx)) != NULL; \
>>  	     idx++)
>>
>> -#define kvm_for_each_memslot(slots, memslot, i)	\
>> -	for (i = 0; i < (slots)->nmemslots &&	\
>> -	      ({ memslot = &(slots)->memslots[i]; 1; }); i++)
>> +#define kvm_for_each_memslot(slots, memslot, i)			\
>> +	for (i = 0; i < KVM_MEM_SLOTS_NUM &&			\
>> +	      ({ memslot = &(slots)->memslots[i]; 1; }) &&	\
>> +	      memslot->npages != 0; i++)
> 
> You might allocate an always-empty memslot at the end and simplify the
> termination condition.
> 


The slots are sorted by its size, all empty slots are at the end of the array,
so we can simplify break the loop if meet a empty slot.

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