Hi Jens, On 5/13/20 1:20 PM, Pekka Enberg wrote:
So I assume if someone does "perf record", they will see significant reduction in page allocator activity with Jens' patch. One possible way around that is forcing the page allocation order to be much higher. IOW, something like the following completely untested patch:
On 5/13/20 11:09 PM, Jens Axboe wrote:
Now tested, I gave it a shot. This seems to bring performance to basically what the io_uring patch does, so that's great! Again, just in the microbenchmark test case, so freshly booted and just running the case.
Great, thanks for testing! On 5/13/20 11:09 PM, Jens Axboe wrote:
Will this patch introduce latencies or non-deterministic behavior for a fragmented system?
You have to talk to someone who is more up-to-date with how the page allocator operates today. But yeah, I assume people still want to avoid higher-order allocations as much as possible, because they make allocation harder when memory is fragmented.
That said, perhaps it's not going to the page allocator as much as I thought, but the problem is that the per-CPU cache size is just to small for these allocations, forcing do_slab_free() to take the slow path often. Would be interesting to know if CONFIG_SLAB does better here because the per-CPU cache size is much larger IIRC.
- Pekka
