On Thu, Jun 15, 2023 at 9:51 AM Jakub Kicinski [off-list ref] wrote:

On Thu, 15 Jun 2023 15:17:39 +0800 Yunsheng Lin wrote:

quoted

quoted

Does hns3_page_order() set a good example for the users?

static inline unsigned int hns3_page_order(struct hns3_enet_ring *ring)
{
#if (PAGE_SIZE < 8192)
    if (ring->buf_size > (PAGE_SIZE / 2))
            return 1;
#endif
    return 0;
}

Why allocate order 1 pages for buffers which would fit in a single page?
I feel like this soft of heuristic should be built into the API itself.

hns3 only support fixed buf size per desc by 512 byte, 1024 bytes, 2048 bytes
4096 bytes, see hns3_buf_size2type(), I think the order 1 pages is for buf size
with 4096 bytes and system page size with 4K, as hns3 driver still support the
per-desc ping-pong way of page splitting when page_pool_enabled is false.

With page pool enabled, you are right that order 0 pages is enough, and I am not
sure about the exact reason we use the some order as the ping-pong way of page
splitting now.
As 2048 bytes buf size seems to be the default one, and I has not heard any one
changing it. Also, it caculates the pool_size using something as below, so the
memory usage is almost the same for order 0 and order 1:

.pool_size = ring->desc_num * hns3_buf_size(ring) /
              (PAGE_SIZE << hns3_page_order(ring)),

I am not sure it worth changing it, maybe just change it to set good example for
the users:) anyway I need to discuss this with other colleague internally and do
some testing before doing the change.

Right, I think this may be a leftover from the page flipping mode of
operation. But AFAIU we should leave the recycling fully to the page
pool now. If we make any improvements try to make them at the page pool
level.

I like your patches as they isolate the drivers from having to make the
fragmentation decisions based on the system page size (4k vs 64k but
we're hearing more and more about ARM w/ 16k pages). For that use case
this is great.

What we don't want is drivers to start requesting larger page sizes
because it looks good in iperf on a freshly booted, idle system :(

Actually that would be a really good direction for this patch set to
look at going into. Rather than having us always allocate a "page" it
would make sense for most drivers to allocate a 4K fragment or the
like in the case that the base page size is larger than 4K. That might
be a good use case to justify doing away with the standard page pool
page and look at making them all fragmented.

In the case of the standard page size being 4K a standard page would
just have to take on the CPU overhead of the atomic_set and
atomic_read for pp_ref_count (new name) which should be minimal as on
most sane systems those just end up being a memory write and read.