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Date: Tue, 13 Jun 2023 21:40:41 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Yunsheng Lin <linyunsheng@huawei.com>
Cc: <davem@davemloft.net>, <pabeni@redhat.com>, <netdev@vger.kernel.org>,
 <linux-kernel@vger.kernel.org>, Lorenzo Bianconi <lorenzo@kernel.org>,
 Alexander Duyck <alexander.duyck@gmail.com>, Jesper Dangaard Brouer
 <hawk@kernel.org>, Ilias Apalodimas <ilias.apalodimas@linaro.org>, Eric
 Dumazet <edumazet@google.com>, Jonathan Corbet <corbet@lwn.net>, Alexei
 Starovoitov <ast@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>, John
 Fastabend <john.fastabend@gmail.com>, <linux-doc@vger.kernel.org>,
 <bpf@vger.kernel.org>
Subject: Re: [PATCH net-next v4 5/5] page_pool: update document about frag
 API
Message-ID: <20230613214041.1c29a357@kernel.org>
In-Reply-To: <20230612130256.4572-6-linyunsheng@huawei.com>
References: <20230612130256.4572-1-linyunsheng@huawei.com>
	<20230612130256.4572-6-linyunsheng@huawei.com>
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On Mon, 12 Jun 2023 21:02:56 +0800 Yunsheng Lin wrote:
> +2. page_pool_alloc_frag(): allocate memory with page splitting when driver knows
> +   that the memory it need is always smaller than or equal to half of the page
> +   allocated from page pool. Page splitting enables memory saving and thus avoid
> +   TLB/cache miss for data access, but there also is some cost to implement page
> +   splitting, mainly some cache line dirtying/bouncing for 'struct page' and
> +   atomic operation for page->pp_frag_count.
> +
> +3. page_pool_alloc(): allocate memory with or without page splitting depending
> +   on the requested memory size when driver doesn't know the size of memory it
> +   need beforehand. It is a mix of the above two case, so it is a wrapper of the
> +   above API to simplify driver's interface for memory allocation with least
> +   memory utilization and performance penalty.

Seems like the semantics of page_pool_alloc() are always better than
page_pool_alloc_frag(). Is there a reason to keep these two separate?