Re: [PATCH v2 09/13] xen/arm: Reduce struct membank size on static shared memory

[Michal Orzel <michal.orzel@xxxxxxx>]

Hi Luca,

On 09/04/2024 13:45, 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
> enum membank_type, with this trick the 'struct membank' has the
> same size with or without the static shared memory, given that
> the 'type' and 'shmem_extra' are never used at the same time,
> hence the 'struct membank' won't grow in size.
> 
> Afterwards, create a new structure 'struct shared_meminfo' which
> has the same interface of 'struct meminfo', but requires less
I would expect some justification for selecting 32 as the max number of shmem 
banks

> banks and hosts the extra information for the static shared memory.
> The fields 'bank' and 'extra' of this structure are meant to be
> linked by the index (e.g. extra[idx] will have the information for
> the bank[idx], for i=0..NR_SHMEM_BANKS), the convinient pointer
> 'shmem_extra' of 'struct membank' is then linked to the related
> 'extra' bank to ease the fruition when a function has access only
> to the 'struct membanks common' of 'struct shared_meminfo'.
> 
> The last part of this work is to move the allocation of the
> static shared memory banks from the 'reserved_mem' to a new
> 'shmem' member of the 'struct bootinfo'.
> Change also the 'shm_mem' member type to be 'struct shared_meminfo'
> in order to match the above changes and allow a memory space
> reduction also in 'struct kernel_info'.
> 
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
With the find_unallocated_memory() issue fixed:
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>

~Michal