[Linaro-mm-sig] Re: [PATCH] mm/vmalloc: map contiguous pages in batches for vmap() whenever possible

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+static inline int get_vmap_batch_order(struct page **pages,

•         unsigned int stride, unsigned int max_steps, unsigned int idx)
  

+{

• int nr_pages = 1;
  

• /*
  

•  * Currently, batching is only supported in vmap_pages_range
  

•  * when page_shift == PAGE_SHIFT.
  

•  */
  

• if (stride != 1)
  

•         return 0;
  

• nr_pages = compound_nr(pages[idx]);
  

• if (nr_pages == 1)
  

•         return 0;
  

• if (max_steps < nr_pages)
  

•         return 0;
  

• if (num_pages_contiguous(&pages[idx], nr_pages) == nr_pages)
  

•         return compound_order(pages[idx]);
  

• return 0;
  

+}

Can we instead look at this as: it can be that we have continues set of pages let's find out. I mean if we do not stick just to compound pages.

We use PageCompound(pages[0]) and compound_nr() as quick filters to skip checking the contiguous count, and this is now the intended use case. Always checking contiguity might cause a slight regression, I guess.

BTW, do we have a strong use case where GFP_COMP or folio is not used, yet the pages are physically contiguous?

Thanks Barry