Re: [PATCH v7 2/2] mm: huge_memory: debugfs for file-backed THP split.

On Mon, Mar 29, 2021 at 11:39:32AM -0400, Zi Yan wrote:

• for (off_cur = off_start; off_cur < off_end;) {

• struct page *fpage = pagecache_get_page(mapping, off_cur,
  

• 				FGP_ENTRY | FGP_HEAD, 0);
  

• if (xa_is_value(fpage) || !fpage) {
  

• 	off_cur += PAGE_SIZE;
  

• 	continue;
  

• }
  

• if (!is_transparent_hugepage(fpage)) {
  

• 	off_cur += PAGE_SIZE;
  

• 	goto next;
  

• }
  

• total++;
  

• off_cur = fpage->index + thp_size(fpage);
  

That can't be right. fpage->index is in units of pages and thp_size is in units of bytes. I wish C had a better type system. I think you meant:

off_cur = fpage->index + thp_nr_pages(fpage);

Also, I think this loop would read better as ...

for (index = off_start; index < off_end; index += nr_pages) { struct page *fpage = pagecache_get_page(mapping, index, FGP_ENTRY | FGP_HEAD, 0); nr_pages = 1; if (xa_is_value(fpage) || !fpage) continue; if (!is_transparent_hugepage(fpage)) goto next; total++; nr_pages = thp_nr_pages(fpage); ...