linux-ext4 - [RFC 06/11] ext4: Add counter to track successful allocation of goal length

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Date:   Fri, 27 Jan 2023 18:07:33 +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-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jan Kara <jack@...e.cz>, Ritesh Harjani <ritesh.list@...il.com>
Subject: [RFC 06/11] ext4: Add counter to track successful allocation of goal length

Track number of allocations where the length of blocks allocated is equal to the
length of goal blocks (post normalization). This metric could be useful if
making changes to the allocator logic in the future as it could give us
visibility into how often do we trim our requests.

PS: ac_b_ex.fe_len might get modified due to preallocation efforts and
hence we use ac_f_ex.fe_len instead since we want to compare how much the
allocator was able to actually find.

Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
---
 fs/ext4/ext4.h    | 1 +
 fs/ext4/mballoc.c | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 4ba2c95915eb..d8fa01e54e81 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1636,6 +1636,7 @@ struct ext4_sb_info {
 	atomic_t s_bal_cX_ex_scanned[EXT4_MB_NUM_CRS];	/* total extents scanned */
 	atomic_t s_bal_groups_scanned;	/* number of groups scanned */
 	atomic_t s_bal_goals;	/* goal hits */
+	atomic_t s_bal_len_goals;	/* len goal hits */
 	atomic_t s_bal_breaks;	/* too long searches */
 	atomic_t s_bal_2orders;	/* 2^order hits */
 	atomic_t s_bal_cr0_bad_suggestions;
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 07a50a13751c..c4ab8f412d32 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2930,6 +2930,7 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
 		   atomic64_read(&sbi->s_bal_cX_failed[CR3]));
 	seq_printf(seq, "\textents_scanned: %u\n", atomic_read(&sbi->s_bal_ex_scanned));
 	seq_printf(seq, "\t\tgoal_hits: %u\n", atomic_read(&sbi->s_bal_goals));
+	seq_printf(seq, "\t\tlen_goal_hits: %u\n", atomic_read(&sbi->s_bal_len_goals));
 	seq_printf(seq, "\t\t2^n_hits: %u\n", atomic_read(&sbi->s_bal_2orders));
 	seq_printf(seq, "\t\tbreaks: %u\n", atomic_read(&sbi->s_bal_breaks));
 	seq_printf(seq, "\t\tlost: %u\n", atomic_read(&sbi->s_mb_lost_chunks));
@@ -4233,6 +4234,8 @@ static void ext4_mb_collect_stats(struct ext4_allocation_context *ac)
 		if (ac->ac_g_ex.fe_start == ac->ac_b_ex.fe_start &&
 				ac->ac_g_ex.fe_group == ac->ac_b_ex.fe_group)
 			atomic_inc(&sbi->s_bal_goals);
+		if (ac->ac_f_ex.fe_len == ac->ac_g_ex.fe_len)
+			atomic_inc(&sbi->s_bal_len_goals);
 		if (ac->ac_found > sbi->s_mb_max_to_scan)
 			atomic_inc(&sbi->s_bal_breaks);
 	}
-- 
2.31.1