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[PATCHv5 08/36] filemap: handle huge pages in do_generic_file_read()

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Most of work happans on head page. Only when we need to do copy data to
userspace we find relevant subpage.

We are still limited by PAGE_SIZE per iteration. Lifting this limitation
would require some more work.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 mm/filemap.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 74341f8b831e..6a2f9ea521fb 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1749,6 +1749,7 @@ static ssize_t do_generic_file_read(struct file *filp, loff_t *ppos,
 			if (unlikely(page == NULL))
 				goto no_cached_page;
 		}
+		page = compound_head(page);
 		if (PageReadahead(page)) {
 			page_cache_async_readahead(mapping,
 					ra, filp, page,
@@ -1830,7 +1831,8 @@ static ssize_t do_generic_file_read(struct file *filp, loff_t *ppos,
 		 * now we can copy it to user space...
 		 */
 
-		ret = copy_page_to_iter(page, offset, nr, iter);
+		ret = copy_page_to_iter(page + index - page->index, offset,
+				nr, iter);
 		offset += ret;
 		index += offset >> PAGE_SHIFT;
 		offset &= ~PAGE_MASK;
@@ -2248,6 +2250,7 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 	 * because there really aren't any performance issues here
 	 * and we need to check for errors.
 	 */
+	page = compound_head(page);
 	ClearPageError(page);
 	error = mapping->a_ops->readpage(file, page);
 	if (!error) {
-- 
2.10.2

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[PATCHv5 00/36] ext4: support of huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:30 +0100
  [PATCHv5 08/36] filemap: handle huge pages in do_generic_file_read() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:30 +0100
  [PATCHv5 04/36] mm, rmap: account file thp pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:30 +0100
  [PATCHv5 02/36] Revert "radix-tree: implement radix_tree_maybe_preload_order()" "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:30 +0100
  [PATCHv5 23/36] mm: account huge pages to dirty, writaback, reclaimable, etc. "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:30 +0100
  [PATCHv5 06/36] thp: handle write-protection faults for file THP "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:30 +0100
  [PATCHv5 35/36] mm, fs, ext4: expand use of page_mapping() and page_to_pgoff() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:30 +0100
  [PATCHv5 33/36] ext4: fix SEEK_DATA/SEEK_HOLE for huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:30 +0100
  [PATCHv5 34/36] ext4: make fallocate() operations work with huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:30 +0100
  [PATCHv5 20/36] truncate: make truncate_inode_pages_range() aware about huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:30 +0100
  [PATCHv5 13/36] mm: make write_cache_pages() work on huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:30 +0100
  [PATCHv5 03/36] page-flags: relax page flag policy for few flags "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:30 +0100
  [PATCHv5 27/36] ext4: handle huge pages in __ext4_block_zero_page_range() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:40 +0100
  [PATCHv5 31/36] ext4: handle writeback with huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:40 +0100
  [PATCHv5 15/36] thp: do not threat slab pages as huge in hpage_{nr_pages,size,mask} "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:40 +0100
  [PATCHv5 32/36] ext4: make EXT4_IOC_MOVE_EXT work with huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:40 +0100
  [PATCHv5 01/36] mm, shmem: swich huge tmpfs to multi-order radix-tree entries "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:40 +0100
  [PATCHv5 30/36] ext4: make ext4_da_page_release_reservation() aware about huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:40 +0100
  [PATCHv5 17/36] fs: make block_read_full_page() be able to read huge page "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:40 +0100
  [PATCHv5 14/36] thp: introduce hpage_size() and hpage_mask() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:40 +0100
  [PATCHv5 18/36] fs: make block_write_{begin,end}() be able to handle huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:40 +0100
  [PATCHv5 24/36] ext4: make ext4_mpage_readpages() hugepage-aware "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:40 +0100
  [PATCHv5 26/36] ext4: handle huge pages in ext4_page_mkwrite() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:40 +0100
  [PATCHv5 21/36] truncate: make invalidate_inode_pages2_range() aware about huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:40 +0100
  [PATCHv5 19/36] fs: make block_page_mkwrite() aware about huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-11-29 12:40 +0100

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