Re: [PATCH 08/11] xen/arm: Reduce struct membank size on static shared memory

[Luca Fancellu <Luca.Fancellu@xxxxxxx>]

> On 22 Mar 2024, at 10:30, Michal Orzel <michal.orzel@xxxxxxx> wrote:
> 
> Hi Luca,
> 
> On 12/03/2024 14:03, Luca Fancellu wrote:
>> 
>> 
>> Currently the memory footprint of the static shared memory feature
>> is impacting all the struct meminfo instances with memory space
>> that is not going to be used.
>> 
>> To solve this issue, rework the static shared memory extra
>> information linked to the memory bank to another structure,
>> struct shmem_membank_extra, and exploit the struct membank
>> padding to host a pointer to that structure in a union with the
> NIT: AFAICT the padding will be reused on Arm64 but on Arm32 there will still 
> be 4B padding.

Yes, my purpose was to make clear that no additional space was needed
for that pointer, should I rephrase it or it’s ok?


>> 
>> 
>> +struct shared_meminfo {
>> +    struct membanks common;
>> +    struct membank bank[NR_SHMEM_BANKS];
>> +    struct shmem_membank_extra extra[NR_SHMEM_BANKS];
>> +};
> Same as with meminfo, please add a BUILD_BUG_ON for padding between common 
> and bank.

Sure

>> 
>> 
>> -static int __init append_shm_bank_to_domain(struct membanks *shm_mem,
>> -                                            paddr_t start, paddr_t size,
>> -                                            const char *shm_id)
>> +static int __init
>> +append_shm_bank_to_domain(struct shared_meminfo *kinfo_shm_mem, paddr_t 
>> start,
> Is there any particular reason to prepend the shm_mem name with kinfo?

I think because usually kinfo is used to point to ’struct kernel_info’, instead 
here we point to
'struct shared_meminfo'

> 
> ~Michal