On 11.04.22 20:18, Vlastimil Babka wrote: > On 3/29/22 18:04, David Hildenbrand wrote: >> ... and move the special check for pinned pages into >> page_try_dup_anon_rmap() to prepare for tracking exclusive anonymous >> pages via a new pageflag, clearing it only after making sure that there >> are no GUP pins on the anonymous page. >> >> We really only care about pins on anonymous pages, because they are >> prone to getting replaced in the COW handler once mapped R/O. For !anon >> pages in cow-mappings (!VM_SHARED && VM_MAYWRITE) we shouldn't really >> care about that, at least not that I could come up with an example. >> >> Let's drop the is_cow_mapping() check from page_needs_cow_for_dma(), as we >> know we're dealing with anonymous pages. Also, drop the handling of >> pinned pages from copy_huge_pud() and add a comment if ever supporting >> anonymous pages on the PUD level. >> >> This is a preparation for tracking exclusivity of anonymous pages in >> the rmap code, and disallowing marking a page shared (-> failing to >> duplicate) if there are GUP pins on a page. >> >> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> > > Acked-by: Vlastimil Babka <vbabka@xxxxxxx> > > Nit: > >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -825,7 +825,8 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, >> */ >> get_page(page); >> rss[mm_counter(page)]++; >> - page_dup_rmap(page, false); >> + /* Cannot fail as these pages cannot get pinned. */ >> + BUG_ON(page_try_dup_anon_rmap(page, false, src_vma)); > > Should we just call __page_dup_rmap() here? This is block for the condition > is_device_private_entry(), and page_try_dup_anon_rmap() can't return -EBUSY > for is_device_private_page(). Hi Vlastimil, thanks for your review! We want to keep page_try_dup_anon_rmap() here, because we extend page_try_dup_anon_rmap() in patch #12 to properly clear PageAnonExclusive() of there are no GUP pins. Just like with current page_try_dup_anon_rmap(), that can't fail for device private pages. -- Thanks, David / dhildenb
