ext4: fallback to complex scan if aligned scan doesn't work

jira LE-3187
Rebuild_History Non-Buildable kernel-5.14.0-570.19.1.el9_6
commit-author Ojaswin Mujoo <ojaswin@linux.ibm.com>
commit 1f6bc02
Empty-Commit: Cherry-Pick Conflicts during history rebuild.
Will be included in final tarball splat. Ref for failed cherry-pick at:
ciq/ciq_backports/kernel-5.14.0-570.19.1.el9_6/1f6bc02f.failed

Currently in case the goal length is a multiple of stripe size we use
ext4_mb_scan_aligned() to find the stripe size aligned physical blocks.
In case we are not able to find any, we again go back to calling
ext4_mb_choose_next_group() to search for a different suitable block
group. However, since the linear search always begins from the start,
most of the times we end up with the same BG and the cycle continues.

With large fliesystems, the CPU can be stuck in this loop for hours
which can slow down the whole system. Hence, until we figure out a
better way to continue the search (rather than starting from beginning)
in ext4_mb_choose_next_group(), lets just fallback to
ext4_mb_complex_scan_group() in case aligned scan fails, as it is much
more likely to find the needed blocks.

	Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
	Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/ee033f6dfa0a7f2934437008a909c3788233950f.1702455010.git.ojaswin@linux.ibm.com
	Signed-off-by: Theodore Ts'o <tytso@mit.edu>
(cherry picked from commit 1f6bc02)
	Signed-off-by: Jonathan Maple <jmaple@ciq.com>

# Conflicts:
#	fs/ext4/mballoc.c

Author: PlaidCat

ciq/ciq_backports/kernel-5.14.0-570.19.1.el9_6/1f6bc02f.failed

@@ -0,0 +1,70 @@
+ext4: fallback to complex scan if aligned scan doesn't work
+
+jira LE-3187
+Rebuild_History Non-Buildable kernel-5.14.0-570.19.1.el9_6
+commit-author Ojaswin Mujoo <ojaswin@linux.ibm.com>
+commit 1f6bc02f18489b9c9ea39b068d0695fb0e4567e9
+Empty-Commit: Cherry-Pick Conflicts during history rebuild.
+Will be included in final tarball splat. Ref for failed cherry-pick at:
+ciq/ciq_backports/kernel-5.14.0-570.19.1.el9_6/1f6bc02f.failed
+
+Currently in case the goal length is a multiple of stripe size we use
+ext4_mb_scan_aligned() to find the stripe size aligned physical blocks.
+In case we are not able to find any, we again go back to calling
+ext4_mb_choose_next_group() to search for a different suitable block
+group. However, since the linear search always begins from the start,
+most of the times we end up with the same BG and the cycle continues.
+
+With large fliesystems, the CPU can be stuck in this loop for hours
+which can slow down the whole system. Hence, until we figure out a
+better way to continue the search (rather than starting from beginning)
+in ext4_mb_choose_next_group(), lets just fallback to
+ext4_mb_complex_scan_group() in case aligned scan fails, as it is much
+more likely to find the needed blocks.
+
+	Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
+	Reviewed-by: Jan Kara <jack@suse.cz>
+Link: https://lore.kernel.org/r/ee033f6dfa0a7f2934437008a909c3788233950f.1702455010.git.ojaswin@linux.ibm.com
+	Signed-off-by: Theodore Ts'o <tytso@mit.edu>
+(cherry picked from commit 1f6bc02f18489b9c9ea39b068d0695fb0e4567e9)
+	Signed-off-by: Jonathan Maple <jmaple@ciq.com>
+
+# Conflicts:
+#	fs/ext4/mballoc.c
+diff --cc fs/ext4/mballoc.c
+index 7f56e4c1f4c7,ebbceb2bac4d..000000000000
+--- a/fs/ext4/mballoc.c
++++ b/fs/ext4/mballoc.c
+@@@ -2784,14 -2887,21 +2784,30 @@@ repeat
+  			}
+  
+  			ac->ac_groups_scanned++;
+ -			if (cr == CR_POWER2_ALIGNED)
+ +			if (cr == 0)
+  				ext4_mb_simple_scan_group(ac, &e4b);
+++<<<<<<< HEAD
+ +			else if (cr == 1 && sbi->s_stripe &&
+ +				 !(ac->ac_g_ex.fe_len %
+ +				 EXT4_B2C(sbi, sbi->s_stripe)))
+ +				ext4_mb_scan_aligned(ac, &e4b);
+ +			else
+ +				ext4_mb_complex_scan_group(ac, &e4b);
+++=======
++ 			else {
++ 				bool is_stripe_aligned = sbi->s_stripe &&
++ 					!(ac->ac_g_ex.fe_len %
++ 					  EXT4_B2C(sbi, sbi->s_stripe));
++ 
++ 				if ((cr == CR_GOAL_LEN_FAST ||
++ 				     cr == CR_BEST_AVAIL_LEN) &&
++ 				    is_stripe_aligned)
++ 					ext4_mb_scan_aligned(ac, &e4b);
++ 
++ 				if (ac->ac_status == AC_STATUS_CONTINUE)
++ 					ext4_mb_complex_scan_group(ac, &e4b);
++ 			}
+++>>>>>>> 1f6bc02f1848 (ext4: fallback to complex scan if aligned scan doesn't work)
+  
+  			ext4_unlock_group(sb, group);
+  			ext4_mb_unload_buddy(&e4b);
+* Unmerged path fs/ext4/mballoc.c