[LU-6770] use per_cpu request pool osc_rq_pools

• Type: Improvement
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.8.0
• Labels: patch
• Assignee: Yang Sheng
• Reporter: Wang Shilong (Inactive)

Description

With many OSCs, the osc will pre-alloc memory at start.
That will occupy the memory of application, especially when the
client need to interact with hundreds of OSTs.

We can solve it by using a golbal per_cpu pool 'osc_rq_pools' rather than
local pool for per osc to change this situation. The upper limit
size of requests in pools is about 1 percent of the total memory.

Also, administrator can use a module parameter to limit the momory
usage by:
options osc osc_reqpool_mem_max=num
The unit of num is MB, and the upper limit will be:
MIN(num, 1% total memory)