ramfs: convert ramfs_nommu_get_unmapped_area() to use filemap_get_folios_contig()

Convert to use folios throughout.  This is in preparation for the removal
for find_get_pages_contig().  Now also supports large folios.

The initial version of this function set the page_address to be returned
after finishing all the checks.  Since folio_batches have a maximum of 15
folios, the function had to be modified to support getting and checking up
to lpages, 15 pages at a time while still returning the initial page
address.  Now the function sets ret as soon as the first batch arrives,
and updates it only if a check fails.

The physical adjacency check utilizes the page frame numbers.  The page
frame number of each folio must be nr_pages away from the first folio.

Link: https://lkml.kernel.org/r/20220824004023.77310-7-vishal.moola@gmail.comSigned-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Chris Mason <clm@fb.com>
Cc: David Sterba <dsterba@suse.com>
Cc: David Sterba <dsterb@suse.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/ramfs/file-nommu.c

@@ -203,9 +203,9 @@ static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
 					    unsigned long addr, unsigned long len,
 					    unsigned long pgoff, unsigned long flags)
 {
-	unsigned long maxpages, lpages, nr, loop, ret;
+	unsigned long maxpages, lpages, nr_folios, loop, ret, nr_pages, pfn;
 	struct inode *inode = file_inode(file);
-	struct page **pages = NULL, **ptr, *page;
+	struct folio_batch fbatch;
 	loff_t isize;
 
 	/* the mapping mustn't extend beyond the EOF */
@@ -221,31 +221,39 @@ static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
 		goto out;
 
 	/* gang-find the pages */
-	pages = kcalloc(lpages, sizeof(struct page *), GFP_KERNEL);
-	if (!pages)
-		goto out_free;
-
-	nr = find_get_pages_contig(inode->i_mapping, pgoff, lpages, pages);
-	if (nr != lpages)
-		goto out_free_pages; /* leave if some pages were missing */
+	folio_batch_init(&fbatch);
+	nr_pages = 0;
+repeat:
+	nr_folios = filemap_get_folios_contig(inode->i_mapping, &pgoff,
+			ULONG_MAX, &fbatch);
+	if (!nr_folios) {
+		ret = -ENOSYS;
+		return ret;
+	}
 
+	if (ret == -ENOSYS) {
+		ret = (unsigned long) folio_address(fbatch.folios[0]);
+		pfn = folio_pfn(fbatch.folios[0]);
+	}
 	/* check the pages for physical adjacency */
-	ptr = pages;
-	page = *ptr++;
-	page++;
-	for (loop = lpages; loop > 1; loop--)
-		if (*ptr++ != page++)
-			goto out_free_pages;
+	for (loop = 0; loop < nr_folios; loop++) {
+		if (pfn + nr_pages != folio_pfn(fbatch.folios[loop])) {
+			ret = -ENOSYS;
+			goto out_free; /* leave if not physical adjacent */
+		}
+		nr_pages += folio_nr_pages(fbatch.folios[loop]);
+		if (nr_pages >= lpages)
+			goto out_free; /* successfully found desired pages*/
+	}
 
+	if (nr_pages < lpages) {
+		folio_batch_release(&fbatch);
+		goto repeat; /* loop if pages are missing */
+	}
 	/* okay - all conditions fulfilled */
-	ret = (unsigned long) page_address(pages[0]);
 
-out_free_pages:
-	ptr = pages;
-	for (loop = nr; loop > 0; loop--)
-		put_page(*ptr++);
 out_free:
-	kfree(pages);
+	folio_batch_release(&fbatch);
 out:
 	return ret;
 }