Re: [PATCH v6 1/1] kasan: Avoid sleepable page allocation from atomic context

On Fri, May 09, 2025 at 07:05:56PM +0900, Harry Yoo wrote:

...

• while (nr_total) {

• nr_pages = min(nr_total, PAGE_SIZE / sizeof(data.pages[0]));
  

• nr_populated = alloc_pages_bulk(GFP_KERNEL, nr_pages, data.pages);
  

• if (nr_populated != nr_pages) {
  

• 	free_pages_bulk(data.pages, nr_populated);
  

• 	free_page((unsigned long)data.pages);
  

• 	return -ENOMEM;
  

• }
  

• data.start = start;
  

• ret = apply_to_page_range(&init_mm, start, nr_pages * PAGE_SIZE,
  

• 			  kasan_populate_vmalloc_pte, &data);
  

• free_pages_bulk(data.pages, nr_pages);
  

A minor suggestion:

I think this free_pages_bulk() can be moved outside the loop (but with PAGE_SIZE / sizeof(data.pages[0]) instead of nr_pages),

Because we know the number of populated pages I think we could use it instead of maximal (PAGE_SIZE / sizeof(data.pages[0])).

because alloc_pages_bulk() simply skips allocating pages for any non-NULL entries.

If some pages in the array were not used, it doesn't have to be freed; on the next iteration of the loop alloc_pages_bulk() can skip allocating pages for the non-NULL entries.

Thanks for the suggestion! I will send an updated version.