On 2023/10/17 23:13, Jakub Kicinski wrote:

On Tue, 17 Oct 2023 15:56:48 +0800 Yunsheng Lin wrote:

quoted

quoted

And I can't figure out now what the "cache" in the name is referring to.
Looks like these are just convenience wrappers which return VA instead
of struct page..  

Yes, it is corresponding to some API like napi_alloc_frag() returning va
instead of 'struct page' mentioned in patch 5.

Anyway, naming is hard, any suggestion for a better naming is always
welcomed:)

I'd just throw a _va (for virtual address) at the end. And not really

_va seems fine:)

mention it in the documentation. Plus the kdoc of the function should
say that this is just a thin wrapper around other page pool APIs, and
it's safe to mix it with other page pool APIs?

I am not sure I understand what do 'safe' and 'mix' mean here.

For 'safe' part, I suppose you mean if there is a va accociated with
a 'struct page' without calling some API like kmap()? For that, I suppose
it is safe when the driver is calling page_pool API without the
__GFP_HIGHMEM flag. Maybe we should mention that in the kdoc and give a
warning if page_pool_*alloc_va() is called with the __GFP_HIGHMEM flag?

For the 'mix', I suppose you mean the below:
1. Allocate a page with the page_pool_*alloc_va() API and free a page with
   page_pool_free() API.
2. Allocate a page with the page_pool_*alloc() API and free a page with
   page_pool_free_va() API.

For 1, it seems it is ok as some virt_to_head_page() and page_address() call
between va and 'struct page' does not seem to change anything if we have
enforce page_pool_*alloc_va() to be called without the __GFP_HIGHMEM flag.

For 2, If the va is returned from page_address() which the allocation API is
called without __GFP_HIGHMEM flag. If not, the va is from kmap*()? which means
we may be calling page_pool_free_va() before kunmap*()? Is that possible?

.

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