Perform whole-page page truncation for hole-punching under a range lock

As an attempt to perform the page truncation more optimally, the
hole-punching support added in 223df0161fad50f53a8fa5ffeea8cc4f8137d522
truncated performed the operation in two steps: first, sub-page "stubs"
were zeroed under the range lock in zfs_free_range() using the new
zfs_zero_partial_page() function and then the whole pages were truncated
within zfs_freesp().  This left a window of opportunity during which
the full pages could be touched.

This patch closes the window by moving the whole-page truncation into
zfs_free_range() under the range lock.

Signed-off-by: Tim Chase <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #2733

1 files changed, 8 insertions, 22 deletions

diff --git a/module/zfs/zfs_znode.c b/module/zfs/zfs_znode.c
index 08faf0838..90dbfd315 100644
--- a/module/zfs/zfs_znode.c
+++ b/module/zfs/zfs_znode.c
@@ -1440,6 +1440,13 @@ zfs_free_range(znode_t *zp, uint64_t off, uint64_t len)
 		/* offset of last_page */
 		last_page_offset = last_page << PAGE_CACHE_SHIFT;
 
+		/* truncate whole pages */
+		if (last_page_offset > first_page_offset) {
+			truncate_inode_pages_range(ZTOI(zp)->i_mapping,
+			    first_page_offset, last_page_offset - 1);
+		}
+
+		/* truncate sub-page ranges */
 		if (first_page > last_page) {
 			/* entire punched area within a single page */
 			zfs_zero_partial_page(zp, off, len);
@@ -1607,31 +1614,10 @@ out:
 	/*
 	 * Truncate the page cache - for file truncate operations, use
 	 * the purpose-built API for truncations.  For punching operations,
-	 * truncate only whole pages within the region; partial pages are
-	 * zeroed under a range lock in zfs_free_range().
+	 * the truncation is handled under a range lock in zfs_free_range.
 	 */
 	if (len == 0)
 		truncate_setsize(ZTOI(zp), off);
-	else if (zp->z_is_mapped) {
-		loff_t first_page, last_page;
-		loff_t first_page_offset, last_page_offset;
-
-		/* first possible full page in hole */
-		first_page = (off + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
-		/* last page of hole */
-		last_page = (off + len) >> PAGE_CACHE_SHIFT;
-
-		/* offset of first_page */
-		first_page_offset = first_page << PAGE_CACHE_SHIFT;
-		/* offset of last_page */
-		last_page_offset = last_page << PAGE_CACHE_SHIFT;
-
-		/* truncate whole pages */
-		if (last_page_offset > first_page_offset) {
-			truncate_inode_pages_range(ZTOI(zp)->i_mapping,
-			    first_page_offset, last_page_offset - 1);
-		}
-	}
 	return (error);
 }