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

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/6642

JIRA: https://issues.redhat.com/browse/RHEL-83284
Conflicts: Work around allocation criteria logic difference and lack
	of macros in RHEL9.

commit 1f6bc02
Author: Ojaswin Mujoo <[email protected]>
Date:   Fri Dec 15 16:49:50 2023 +0530

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

    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 <[email protected]>
    Reviewed-by: Jan Kara <[email protected]>
    Link: https://lore.kernel.org/r/ee033f6dfa0a7f2934437008a909c3788233950f.1702455010.git.ojaswin@linux.ibm.com
    Signed-off-by: Theodore Ts'o <[email protected]>

Signed-off-by: Brian Foster <[email protected]>

Approved-by: Eric Sandeen <[email protected]>
Approved-by: Carlos Maiolino <[email protected]>
Approved-by: Jay Shin <[email protected]>
Approved-by: CKI KWF Bot <[email protected]>

Merged-by: Augusto Caringi <[email protected]>

Author: caringi

fs/ext4/mballoc.c

@@ -2786,12 +2786,17 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
 			ac->ac_groups_scanned++;
 			if (cr == 0)
 				ext4_mb_simple_scan_group(ac, &e4b);
-			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 == 1 && is_stripe_aligned)
+					ext4_mb_scan_aligned(ac, &e4b);
+
+				if (ac->ac_status == AC_STATUS_CONTINUE)
+					ext4_mb_complex_scan_group(ac, &e4b);
+			}
 
 			ext4_unlock_group(sb, group);
 			ext4_mb_unload_buddy(&e4b);