netdev - Re: [PATCH v7 07/15] net: page_pool: introduce page_pool_mp_return_in

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Message-ID: <CAHS8izPRvrCA9Ffg8KpZ0NtW8mv3GB=if=JZ4tYHK9c2zU++Ow@mail.gmail.com>
Date: Fri, 1 Nov 2024 13:05:09 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: David Wei <dw@...idwei.uk>
Cc: io-uring@...r.kernel.org, netdev@...r.kernel.org, 
	Jens Axboe <axboe@...nel.dk>, Pavel Begunkov <asml.silence@...il.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, David Ahern <dsahern@...nel.org>, 
	Stanislav Fomichev <stfomichev@...il.com>, Joe Damato <jdamato@...tly.com>, 
	Pedro Tammela <pctammela@...atatu.com>
Subject: Re: [PATCH v7 07/15] net: page_pool: introduce page_pool_mp_return_in_cache

On Tue, Oct 29, 2024 at 4:06 PM David Wei <dw@...idwei.uk> wrote:
>
> From: Pavel Begunkov <asml.silence@...il.com>
>
> Add a helper that allows a page pool memory provider to efficiently
> return a netmem off the allocation callback.
>
> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
> Signed-off-by: David Wei <dw@...idwei.uk>
> ---
>  include/net/page_pool/memory_provider.h |  4 ++++
>  net/core/page_pool.c                    | 19 +++++++++++++++++++
>  2 files changed, 23 insertions(+)
>
> diff --git a/include/net/page_pool/memory_provider.h b/include/net/page_pool/memory_provider.h
> index 83d7eec0058d..352b3a35d31c 100644
> --- a/include/net/page_pool/memory_provider.h
> +++ b/include/net/page_pool/memory_provider.h
> @@ -1,3 +1,5 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +
>  #ifndef _NET_PAGE_POOL_MEMORY_PROVIDER_H
>  #define _NET_PAGE_POOL_MEMORY_PROVIDER_H
>
> @@ -7,4 +9,6 @@ int page_pool_mp_init_paged_area(struct page_pool *pool,
>  void page_pool_mp_release_area(struct page_pool *pool,
>                                 struct net_iov_area *area);
>
> +void page_pool_mp_return_in_cache(struct page_pool *pool, netmem_ref netmem);
> +
>  #endif
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index 8bd4a3c80726..9078107c906d 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -1213,3 +1213,22 @@ void page_pool_mp_release_area(struct page_pool *pool,
>                 page_pool_release_page_dma(pool, net_iov_to_netmem(niov));
>         }
>  }
> +
> +/*
> + * page_pool_mp_return_in_cache() - return a netmem to the allocation cache.
> + * @pool:      pool from which pages were allocated
> + * @netmem:    netmem to return
> + *
> + * Return already allocated and accounted netmem to the page pool's allocation
> + * cache. The function doesn't provide synchronisation and must only be called
> + * from the napi context.

Maybe add:

/* Caller must verify that there is room in the cache */

> + */
> +void page_pool_mp_return_in_cache(struct page_pool *pool, netmem_ref netmem)
> +{
> +       if (WARN_ON_ONCE(pool->alloc.count >= PP_ALLOC_CACHE_REFILL))
> +               return;

The caller must verify this anyway, right? so maybe this WARN_ON_ONCE
is too defensive.

> +
> +       page_pool_dma_sync_for_device(pool, netmem, -1);
> +       page_pool_fragment_netmem(netmem, 1);
> +       pool->alloc.cache[pool->alloc.count++] = netmem;
> +}
> --
> 2.43.5
>


-- 
Thanks,
Mina