Re: [PATCH net-next v4 4/5] page_pool: remove PP_FLAG_PAGE_FRAG flag

[Yunsheng Lin <yunshenglin0825@gmail.com>]

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 For a bit of historical reference on igb/ixgbe they had a known issue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?