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@linux.ibm.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/343620e2be8a237239ea2613a7a866ee8607e973.1685449706.git.ojaswin@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 34ec65126ea778ef1280ffe106f3da12ec81a214..e4f53947f51ff1019caf8a717ed91917a1826a72 100644 (file)
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1558,6 +1558,7 @@ 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 e28731426ee54bd6282381175b1796f7222e3fbe..64d3760e4bcf128d4c5d90886137455e837b0eaa 100644 (file)
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2965,6 +2965,7 @@ 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));
@@ -4410,6 +4411,8 @@ 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);
        }