22.07.2021 15:29, Matthew Wilcox пишет:

On Thu, Jul 22, 2021 at 02:52:28PM +0300, Dmitry Osipenko wrote:

...

The obvious solution is just to change folio_copy():

 {
-       unsigned i, nr = folio_nr_pages(src);
+       unsigned i = 0;
+       unsigned nr = folio_nr_pages(src);

-       for (i = 0; i < nr; i++) {
-               cond_resched();
+       for (;;) {
                copy_highpage(folio_page(dst, i), folio_page(src, i));
+               if (i++ == nr)

This works with the ++i precedence change. Thanks!

+                       break;
+               cond_resched();
        }
 }

now it only calls cond_resched() for multi-page folios.

...

Thank you for the explanation and for the fix!

The fs/ and mm/ are mostly outside of my scope, hope you'll figure out
the buffer-head case soon.