Hi,
I recently discovered GFS2 was writing the log descriptor items in
the journal in reverse order. For example, if I do a bunch of file
creates, the result was a log header that looked something like this:
0x298 (j+ 242): Log descriptor, type 300 (Metadata) len:504, data1: 503
0xa6e9ce di 0xa6e9a7 di 0xa6e97b di 0xa6e942 di
0xa6e911 di 0xa6e8d2 di 0xa6e898 di 0xa6e86e di
0xa6e840 di 0xa6e809 di 0xa6e7d7 di 0xa6e77e di
0xa6e747 di 0xa6e721 di 0xa6e6f8 di 0xa6e6ca di
0xa6e680 di 0xa6e63d di 0xa6e619 di 0xa6e5f4 di
0xa6e5d1 di 0xa6e598 di 0xa6e520 di 0xa6e4f4 di
0xa6e4c1 di 0xa6e489 di 0xa6e45c di 0xa6e427 di
As you can see, the blocks are reverse-sorted. This patch changes the
order so that they're written in sorted order. Log headers written with
the patch look more like this:
0x36e (j+ 318): Log descriptor, type 300 (Metadata) len:504, data1: 503
0x4d5a80 di 0x4d5aa0 lf 0x4d5aa1 di 0x4d5aa2 di
0x4d5aa3 di 0x4d5aa4 di 0x4d5aa5 di 0x4d5aa6 di
0x4d5aa7 di 0x4d5aa8 di 0x4d5aa9 di 0x4d5aaa di
0x4d5aab di 0x4d5aac di 0x4d5aad di 0x4d5aae di
0x4d5aaf di 0x4d5ab0 di 0x4d5ab1 di 0x4d5ab2 di
0x4d5ab3 di 0x4d5ab4 di 0x4d5ab5 di 0x4d5ab6 di
0x4d5ab7 di 0x4d5ab8 di 0x4d5ab9 di 0x4d5aba di
The blocks following the log descriptor are written sequentially, so the
sort order won't affect performance at all, but it makes the journal
easier to decipher for debugging purposes.
Patch description:
This patch changes the order in which the blocks are processed by function
gfs2_before_commit. Before, it was processing them in the wrong order such
that the blocks would be layed out and written in reverse order. This
changes the order to the correct order.
Regards,
Bob Peterson
Red Hat File Systems
Signed-off-by: Bob Peterson <rpete...@redhat.com>
---
diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
index 2c1ae86..d644470 100644
--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -444,7 +444,7 @@ static void gfs2_before_commit(struct gfs2_sbd *sdp,
unsigned int limit,
ptr = (__be64 *)(ld + 1);
n = 0;
- list_for_each_entry_continue(bd1, blist, bd_list) {
+ list_for_each_entry_continue_reverse(bd1, blist, bd_list) {
*ptr++ = cpu_to_be64(bd1->bd_bh->b_blocknr);
if (is_databuf) {
gfs2_check_magic(bd1->bd_bh);
@@ -459,7 +459,7 @@ static void gfs2_before_commit(struct gfs2_sbd *sdp,
unsigned int limit,
gfs2_log_lock(sdp);
n = 0;
- list_for_each_entry_continue(bd2, blist, bd_list) {
+ list_for_each_entry_continue_reverse(bd2, blist, bd_list) {
get_bh(bd2->bd_bh);
gfs2_log_unlock(sdp);
lock_buffer(bd2->bd_bh);
