netdev - Re: [PATCH net-next v4 4/5] page_pool: remove PP_FLAG_PAGE

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Date: Sat, 17 Jun 2023 20:19:46 +0800
From: Yunsheng Lin <yunshenglin0825@...il.com>
To: Alexander Duyck <alexander.duyck@...il.com>,
 Yunsheng Lin <linyunsheng@...wei.com>
Cc: Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net, pabeni@...hat.com,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 Lorenzo Bianconi <lorenzo@...nel.org>, Yisen Zhuang
 <yisen.zhuang@...wei.com>, Salil Mehta <salil.mehta@...wei.com>,
 Eric Dumazet <edumazet@...gle.com>, Sunil Goutham <sgoutham@...vell.com>,
 Geetha sowjanya <gakula@...vell.com>, Subbaraya Sundeep
 <sbhatta@...vell.com>, hariprasad <hkelam@...vell.com>,
 Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>,
 Felix Fietkau <nbd@....name>, Ryder Lee <ryder.lee@...iatek.com>,
 Shayne Chen <shayne.chen@...iatek.com>, Sean Wang <sean.wang@...iatek.com>,
 Kalle Valo <kvalo@...nel.org>, Matthias Brugger <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 Ilias Apalodimas <ilias.apalodimas@...aro.org>, linux-rdma@...r.kernel.org,
 linux-wireless@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH net-next v4 4/5] page_pool: remove PP_FLAG_PAGE_FRAG flag

On 2023/6/16 23:01, Alexander Duyck wrote:

...

>>> 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.
>>
>> I am not sure if I understand the above, isn't the frag API able to
>> support allocating a 4K fragment when base page size is larger than
>> 4K before or after this patch? what more do we need to do?
> 
> I'm not talking about the frag API. I am talking about the
> non-fragmented case. Right now standard page_pool will allocate an
> order 0 page. So if a driver is using just pages expecting 4K pages
> that isn't true on these ARM or PowerPC systems where the page size is
> larger than 4K.
> 
> For a bit of historical reference on igb/ixgbe they had a known issue
> where they would potentially run a system out of memory when page size
> was larger than 4K. I had originally implemented things with just the
> refcounting hack and at the time it worked great on systems with 4K
> pages. However on a PowerPC it would trigger OOM errors because they
> could run with 64K pages. To fix that I started adding all the
> PAGE_SIZE checks in the driver and moved over to a striping model for
> those that would free the page when it reached the end in order to
> force it to free the page and make better use of the available memory.

Isn't the page_pool_alloc() or page_pool_alloc_frag() API also solve
the above problem?
I think what you really want is another layer of subdividing support
in the driver on top of the above, right?