buffer: Rewrite nobh_truncate_page() to use folios

 - Calculate iblock directly instead of using a while loop
 - Move has_buffers to the end to remove a backwards jump
 - Use __filemap_get_folio() instead of grab_cache_page(), which
   removes a spurious FGP_ACCESSED flag.
 - Eliminate length and pos variables
 - Use folio APIs where they exist

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --git a/fs/buffer.c b/fs/buffer.c
index fb4df259c92da4c4d1033965ff634b3ba9743df6..9737e0dbe3ec62d5c2ca683cb677d9749094db08 100644 (file)
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2791,44 +2791,28 @@ int nobh_truncate_page(struct address_space *mapping,
                        loff_t from, get_block_t *get_block)
 {
        pgoff_t index = from >> PAGE_SHIFT;
-       unsigned offset = from & (PAGE_SIZE-1);
-       unsigned blocksize;
-       sector_t iblock;
-       unsigned length, pos;
        struct inode *inode = mapping->host;
-       struct page *page;
+       unsigned blocksize = i_blocksize(inode);
+       struct folio *folio;
        struct buffer_head map_bh;
+       size_t offset;
+       sector_t iblock;
        int err;
 
-       blocksize = i_blocksize(inode);
-       length = offset & (blocksize - 1);
-
        /* Block boundary? Nothing to do */
-       if (!length)
+       if (!(from & (blocksize - 1)))
                return 0;
 
-       length = blocksize - length;
-       iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
-
-       page = grab_cache_page(mapping, index);
+       folio = __filemap_get_folio(mapping, index, FGP_LOCK | FGP_CREAT,
+                       mapping_gfp_mask(mapping));
        err = -ENOMEM;
-       if (!page)
+       if (!folio)
                goto out;
 
-       if (page_has_buffers(page)) {
-has_buffers:
-               unlock_page(page);
-               put_page(page);
-               return block_truncate_page(mapping, from, get_block);
-       }
-
-       /* Find the buffer that contains "offset" */
-       pos = blocksize;
-       while (offset >= pos) {
-               iblock++;
-               pos += blocksize;
-       }
+       if (folio_buffers(folio))
+               goto has_buffers;
 
+       iblock = from >> inode->i_blkbits;
        map_bh.b_size = blocksize;
        map_bh.b_state = 0;
        err = get_block(inode, iblock, &map_bh, 0);
@@ -2839,29 +2823,35 @@ has_buffers:
                goto unlock;
 
        /* Ok, it's mapped. Make sure it's up-to-date */
-       if (!PageUptodate(page)) {
-               err = mapping->a_ops->readpage(NULL, page);
+       if (!folio_test_uptodate(folio)) {
+               err = mapping->a_ops->readpage(NULL, &folio->page);
                if (err) {
-                       put_page(page);
+                       folio_put(folio);
                        goto out;
                }
-               lock_page(page);
-               if (!PageUptodate(page)) {
+               folio_lock(folio);
+               if (!folio_test_uptodate(folio)) {
                        err = -EIO;
                        goto unlock;
                }
-               if (page_has_buffers(page))
+               if (folio_buffers(folio))
                        goto has_buffers;
        }
-       zero_user(page, offset, length);
-       set_page_dirty(page);
+       offset = offset_in_folio(folio, from);
+       folio_zero_segment(folio, offset, round_up(offset, blocksize));
+       folio_mark_dirty(folio);
        err = 0;
 
 unlock:
-       unlock_page(page);
-       put_page(page);
+       folio_unlock(folio);
+       folio_put(folio);
 out:
        return err;
+
+has_buffers:
+       folio_unlock(folio);
+       folio_put(folio);
+       return block_truncate_page(mapping, from, get_block);
 }
 EXPORT_SYMBOL(nobh_truncate_page);