Re: [PATCH] x86: shrink 'struct domain', was already PAGE_SIZE

[Corneliu ZUZU <czuzu@bitdefender.com>]

On 2/1/2016 12:47 PM, Jan Beulich wrote:
>>>> On 01.02.16 at 08:42, <czuzu@bitdefender.com> wrote:
>> The X86 domain structure already occupied PAGE_SIZE (4096).
>>
>> Looking @ the memory layout of the structure, we could see that
>> overall most was occupied by (used the pahole tool on domain.o):
>>   * sizeof(domain.arch) = sizeof(arch_domain) = 3328 bytes.
>>   * sizeof(domain.arch.hvm_domain) = 2224 bytes.
>>   * sizeof(domain.arch.hvm_domain.pl_time) = 1088 bytes.
>> This patch attempts to free some space, by making the pl_time
>> field in hvm_domain dynamically allocated.
>> We xzalloc/xfree it @ hvm_domain_initialise/hvm_domain_destroy.
>>
>> After this change, the domain structure shrunk w/ 1152 bytes (>1K!).
>>
>> Signed-off-by: Corneliu ZUZU <czuzu@bitdefender.com>
> Reviewed-by: Jan Beulich <jbeulich@suse.com>
> albeit ...
>
>> --- a/xen/include/asm-x86/hvm/vpt.h
>> +++ b/xen/include/asm-x86/hvm/vpt.h
>> @@ -139,6 +139,9 @@ struct pl_time {    /* platform time */
>>       /* Ensures monotonicity in appropriate timer modes. */
>>       uint64_t last_guest_time;
>>       spinlock_t pl_time_lock;
>> +    /* pl_time allocated dynamically, need to keep link to
>> +     * containing domain */
>> +    struct domain *domain;
>>   };
> ... I wonder about the usefulness of this (malformed) comment. I'll
> likely ditch it while committing.
>
> Jan
>

Agreed, sorry about that and thanks.

Corneliu.