Hi! I like this patch and am confident with it on x86. However,
a) it has no x86_64 coverage; and b) xfstests xfs/306 in particular
emits more of this output:
buffer_io_error: nnnn callbacks suppressed
Might someone evaluate this patch or the intent of the patch?
The intent:
For XFS filesystems that don't change much, such as the /boot and
alternate / partitions here, mount times were about 17s instead of
0.4s while the log is in a wrapped state, write caches off. This
patch fixes the issue on v4- and v5-superblock XFS filesystems.
xfs_repair can solve this issue short-term and also cut wrapped-log
mount time in half short-term for v5 file systems. Don't know if
that's a mkfs.xfs issue or just coincidence.
A bisect still needs to be done to determine when the slow mount
behavior started. It could very well be that somebody fixed the
buffer_io_error messages that I saw long ago, and the solution made
some mounts here rather miserable.
Thanks!
Michael
The patch:
xlog_write_log_records() has an algorithm to "Greedily allocate a
buffer big enough...," starting with ffs(blocks), adding two sensible
checks, and then feeding it to a loop with checks of its own.
However, when blocks is an odd number, the number that becomes nbblks
to the xlog_bwrite() function ends up being 2 (1 << 1). The most
obvious effect is that when the log wraps, a write of two odd-sized
log regions on an 8-GB XFS filesystem will take around 2049 calls
to xlog_bwrite() instead of the "two separate I/Os" suggested in
xlog_clear_stale_blocks().
Fix this by changing the ffs(blocks) to fls(blocks).
There is a similar ffs(blocks) check in xlog_find_verify_cycle().
This was not investigated.
Signed-off-by: Michael L. Semon <mlsemon35@xxxxxxxxx>
---
fs/xfs/xfs_log_recover.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index a5a945f..13381eb 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -1242,7 +1242,7 @@ xlog_write_log_records(
* a smaller size. We need to be able to write at least a
* log sector, or we're out of luck.
*/
- bufblks = 1 << ffs(blocks);
+ bufblks = 1 << fls(blocks);
while (bufblks > log->l_logBBsize)
bufblks >>= 1;
while (!(bp = xlog_get_bp(log, bufblks))) {
--
1.8.4
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