From: Matthew Wilcox (Oracle) <wi...@infradead.org>
> Sent: 17 April 2021 00:07
>
> The net page_pool wants to use a magic value to identify page pool pages.
> The best place to put it is in the first word where it can be clearly a
> non-pointer value. That means shifting dma_addr up to alias with ->index,
> which means we need to find another way to indicate page_is_pfmemalloc().
> Since page_pool doesn't want to set its magic value on pages which are
> pfmemalloc, we can use bit 1 of compound_head to indicate that the page
> came from the memory reserves.
>
...
> struct { /* page_pool used by netstack */
> - /**
> - * @dma_addr: might require a 64-bit value on
> - * 32-bit architectures.
> - */
> + unsigned long pp_magic;
> + unsigned long xmi;
> + unsigned long _pp_mapping_pad;
> unsigned long dma_addr[2];
> };
You've deleted the comment.
I also think there should be a comment that dma_addr[0]
must be aliased to ->index.
(Or whatever all the exact requirements are.)
David
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