Messages in this thread | | | Date | Thu, 24 Jun 2021 19:02:23 +0100 | From | Matthew Wilcox <> | Subject | Re: [PATCH v2 20/46] mm/migrate: Add folio_migrate_copy() |
| |
On Wed, Jun 23, 2021 at 10:35:00AM +0200, Christoph Hellwig wrote: > > +void folio_migrate_copy(struct folio *newfolio, struct folio *folio) > > { > > + unsigned int i = folio_nr_pages(folio) - 1; > > > > + copy_highpage(folio_page(newfolio, i), folio_page(folio, i)); > > + while (i-- > 0) { > > + cond_resched()a > > + /* folio_page() handles discontinuities in memmap */ > > + copy_highpage(folio_page(newfolio, i), folio_page(folio, i)); > > + } > > + > > What is the advantage of copying backwards here to start with?
Easier to write the loop this way? I suppose we could do it as ...
unsigned int i, nr = folio_nr_pages(folio);
for (i = 0; i < nr; i++) { /* folio_page() handles discontinuities in memmap */ copy_highpage(folio_page(newfolio, i), folio_page(folio, i)); cond_resched(); }
I'm not really bothered. As long as we don't call folio_nr_pages() for each iteration of the loop ... I've actually been wondering about marking that as __pure, but I don't quite have the nerve to do it yet.
| |