Re: [PATCH 00/24] Split page pools from struct page

[Jesper Dangaard Brouer <jbrouer@redhat.com>]

On 30/11/2022 23.07, Matthew Wilcox (Oracle) wrote:
> The MM subsystem is trying to reduce struct page to a single pointer.
> The first step towards that is splitting struct page by its individual
> users, as has already been done with folio and slab.  This attempt chooses
> 'netmem' as a name, but I am not even slightly committed to that name,
> and will happily use another.

I've not been able to come-up with a better name, so I'm okay with
'netmem'.  Others are of-cause free to bikesheet this ;-)

> There are some relatively significant reductions in kernel text
> size from these changes.  I'm not qualified to judge how they
> might affect performance, but every call to put_page() includes
> a call to compound_head(), which is now rather more complex
> than it once was (at least in a distro config which enables
> CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP).
> 

I have a micro-benchmark [1][2], that I want to run on this patchset.
Reducing the asm code 'text' size is less likely to improve a
microbenchmark. The 100Gbit mlx5 driver uses page_pool, so perhaps I can
run a packet benchmark that can show the (expected) performance improvement.

[1] 
https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/bench_page_pool_simple.c
[2] 
https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/bench_page_pool_cross_cpu.c

> I've only converted one user of the page_pool APIs to use the new netmem
> APIs, all the others continue to use the page based ones.
> 

I guess we/netdev-devels need to update the NIC drivers that uses page_pool.

> Uh, I see I left netmem_to_virt() as its own commit instead of squashing
> it into "netmem: Add utility functions".  I'll fix that in the next
> version, because I'm sure you'll want some changes anyway.
> 
> Happy to answer questions.
> 
> Matthew Wilcox (Oracle) (24):
>    netmem: Create new type
>    netmem: Add utility functions
>    page_pool: Add netmem_set_dma_addr() and netmem_get_dma_addr()
>    page_pool: Convert page_pool_release_page() to
>      page_pool_release_netmem()
>    page_pool: Start using netmem in allocation path.
>    page_pool: Convert page_pool_return_page() to
>      page_pool_return_netmem()
>    page_pool: Convert __page_pool_put_page() to __page_pool_put_netmem()
>    page_pool: Convert pp_alloc_cache to contain netmem
>    page_pool: Convert page_pool_defrag_page() to
>      page_pool_defrag_netmem()
>    page_pool: Convert page_pool_put_defragged_page() to netmem
>    page_pool: Convert page_pool_empty_ring() to use netmem
>    page_pool: Convert page_pool_alloc_pages() to page_pool_alloc_netmem()
>    page_pool: Convert page_pool_dma_sync_for_device() to take a netmem
>    page_pool: Convert page_pool_recycle_in_cache() to netmem
>    page_pool: Remove page_pool_defrag_page()
>    page_pool: Use netmem in page_pool_drain_frag()
>    page_pool: Convert page_pool_return_skb_page() to use netmem
>    page_pool: Convert frag_page to frag_nmem
>    xdp: Convert to netmem
>    mm: Remove page pool members from struct page
>    netmem_to_virt
>    page_pool: Pass a netmem to init_callback()
>    net: Add support for netmem in skb_frag
>    mvneta: Convert to netmem
> 
>   drivers/net/ethernet/marvell/mvneta.c |  48 ++---
>   include/linux/mm_types.h              |  22 ---
>   include/linux/skbuff.h                |  11 ++
>   include/net/page_pool.h               | 181 ++++++++++++++---
>   include/trace/events/page_pool.h      |  28 +--
>   net/bpf/test_run.c                    |   4 +-
>   net/core/page_pool.c                  | 274 +++++++++++++-------------
>   net/core/xdp.c                        |   7 +-
>   8 files changed, 344 insertions(+), 231 deletions(-)
> 
> 
> base-commit: 13ee7ef407cfcf63f4f047460ac5bb6ba5a3447d