Re: [PATCH bpf-next 3/5] bpf: Refill only one percpu element in memalloc

[Yonghong Song <yonghong.song@linux.dev>]

On 12/13/23 3:05 AM, Hou Tao wrote:
>
> On 12/13/2023 6:30 AM, Yonghong Song wrote:
>> Typically for percpu map element or data structure, once allocated,
>> most operations are lookup or in-place update. Deletion are really
>> rare. Currently, for percpu data strcture, 4 elements will be
>> refilled if the size is <= 256. Let us just do with one element
>> for percpu data. For example, for size 256 and 128 cpus, the
>> potential saving will be 3 * 256 * 128 * 128 = 12MB.
>>
>> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
>> ---
>>   kernel/bpf/memalloc.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
>> index 84987e97fd0a..a1d718ee264d 100644
>> --- a/kernel/bpf/memalloc.c
>> +++ b/kernel/bpf/memalloc.c
>> @@ -483,11 +483,15 @@ static void init_refill_work(struct bpf_mem_cache *c)
>>   
>>   static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
>>   {
>> +	int cnt = 1;
>> +
>>   	/* To avoid consuming memory assume that 1st run of bpf
>>   	 * prog won't be doing more than 4 map_update_elem from
>>   	 * irq disabled region
>>   	 */
> Please update the comments accordingly.
Ack.
>> -	alloc_bulk(c, c->unit_size <= 256 ? 4 : 1, cpu_to_node(cpu), false);
>> +	if (!c->percpu_size && c->unit_size <= 256)
>> +		cnt = 4;
>> +	alloc_bulk(c, cnt, cpu_to_node(cpu), false);
>>   }
>>   
>>   static int check_obj_size(struct bpf_mem_cache *c, unsigned int idx)