linux-kernel - [PATCH v2] ext4: Replace CR_FAST macro with inline function for readability

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Message-Id: <20230630085927.140137-1-ojaswin@linux.ibm.com>
Date:   Fri, 30 Jun 2023 14:29:27 +0530
From:   Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To:     linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>
Cc:     Ritesh Harjani <riteshh@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>,
        Kemeng Shi <shikemeng@...weicloud.com>
Subject: [PATCH v2] ext4: Replace CR_FAST macro with inline function for readability

Replace CR_FAST with ext4_mb_cr_expensive() inline function for better
readability. This function returns true if the criteria is one of the
expensive/slower ones where lots of disk IO/prefetching is acceptable.

No functional changes are intended in this patch.

Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Reviewed-by: Jan Kara <jack@...e.cz>
---

Changes since v1 [1] 

* reworded an if condition in ext_mb_good_group_nolock
  and added a comment to better describe the intent of the 
	condition
* Picked up RVB from Jan.

[1]
https://lore.kernel.org/linux-ext4/ZJ2YIr5EVbz4ezIc@li-bb2b2a4c-3307-11b2-a85c-8fa5c3a69313.ibm.com/T/#ma9428de15c4084937274f4d66dcd4d53f505d32a

 fs/ext4/ext4.h    |  7 ++++---
 fs/ext4/mballoc.c | 13 +++++++++----
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 45a531446ea2..e404169a2858 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -176,9 +176,6 @@ enum criteria {
 	EXT4_MB_NUM_CRS
 };
 
-/* criteria below which we use fast block scanning and avoid unnecessary IO */
-#define CR_FAST CR_GOAL_LEN_SLOW
-
 /*
  * Flags used in mballoc's allocation_context flags field.
  *
@@ -2924,6 +2921,10 @@ extern int ext4_trim_fs(struct super_block *, struct fstrim_range *);
 extern void ext4_process_freed_data(struct super_block *sb, tid_t commit_tid);
 extern void ext4_mb_mark_bb(struct super_block *sb, ext4_fsblk_t block,
 		       int len, int state);
+static inline bool ext4_mb_cr_expensive(enum criteria cr)
+{
+	return cr >= CR_GOAL_LEN_SLOW;
+}
 
 /* inode.c */
 void ext4_inode_csum_set(struct inode *inode, struct ext4_inode *raw,
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index a2475b8c9fb5..542577f621c6 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2446,7 +2446,7 @@ void ext4_mb_complex_scan_group(struct ext4_allocation_context *ac,
 			break;
 		}
 
-		if (ac->ac_criteria < CR_FAST) {
+		if (!ext4_mb_cr_expensive(ac->ac_criteria)) {
 			/*
 			 * In CR_GOAL_LEN_FAST and CR_BEST_AVAIL_LEN, we are
 			 * sure that this group will have a large enough
@@ -2630,7 +2630,12 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
 	free = grp->bb_free;
 	if (free == 0)
 		goto out;
-	if (cr <= CR_FAST && free < ac->ac_g_ex.fe_len)
+	/*
+	 * In all criterias except CR_ANY_FREE we try to avoid groups that
+	 * can't possibly satisfy the full goal request due to insufficient
+	 * free blocks.
+	 */
+	if (cr < CR_ANY_FREE && free < ac->ac_g_ex.fe_len)
 		goto out;
 	if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
 		goto out;
@@ -2654,7 +2659,7 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
 		 * sure we locate metadata blocks in the first block group in
 		 * the flex_bg if possible.
 		 */
-		if (cr < CR_FAST &&
+		if (!ext4_mb_cr_expensive(cr) &&
 		    (!sbi->s_log_groups_per_flex ||
 		     ((group & ((1 << sbi->s_log_groups_per_flex) - 1)) != 0)) &&
 		    !(ext4_has_group_desc_csum(sb) &&
@@ -2848,7 +2853,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
 			 * spend a lot of time loading imperfect groups
 			 */
 			if ((prefetch_grp == group) &&
-			    (cr >= CR_FAST ||
+			    (ext4_mb_cr_expensive(cr) ||
 			     prefetch_ios < sbi->s_mb_prefetch_limit)) {
 				nr = sbi->s_mb_prefetch;
 				if (ext4_has_feature_flex_bg(sb)) {
-- 
2.31.1