gfs2: Fix metadata read-ahead during truncate (2)

The previous attempt to fix for metadata read-ahead during truncate was
incorrect: for files with a height > 2 (1006989312 bytes with a block
size of 4096 bytes), read-ahead requests were not being issued for some
of the indirect blocks discovered while walking the metadata tree,
leading to significant slow-downs when deleting large files.  Fix that.

In addition, only issue read-ahead requests in the first pass through
the meta-data tree, while deallocating data blocks.

Fixes: c3ce5aa9b0 ("gfs2: Fix metadata read-ahead during truncate")
Cc: stable@vger.kernel.org # v4.16+
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

1 files changed, 10 insertions, 4 deletions

diff --git a/fs/gfs2/bmap.c b/fs/gfs2/bmap.c
index 5f3ea07ef5e2..38d88fcb6988 100644
--- a/fs/gfs2/bmap.c
+++ b/fs/gfs2/bmap.c
@@ -1908,10 +1908,16 @@ static int punch_hole(struct gfs2_inode *ip, u64 offset, u64 length)
                         if (ret < 0)
                                 goto out;
 
-                        /* issue read-ahead on metadata */
-                        if (mp.mp_aheight > 1) {
-                                for (; ret > 1; ret--) {
-                                        metapointer_range(&mp, mp.mp_aheight - ret,
+                        /* On the first pass, issue read-ahead on metadata. */
+                        if (mp.mp_aheight > 1 && strip_h == ip->i_height - 1) {
+                                unsigned int height = mp.mp_aheight - 1;
+
+                                /* No read-ahead for data blocks. */
+                                if (mp.mp_aheight - 1 == strip_h)
+                                        height--;
+
+                                for (; height >= mp.mp_aheight - ret; height--) {
+                                        metapointer_range(&mp, height,
                                                           start_list, start_aligned,
                                                           end_list, end_aligned,
                                                           &start, &end);