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ext4: add mb_debug logging when there are lost chunks

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Lost chunks are when some other process raced with the current thread
to grab a particular block allocation.  Add mb_debug log for
developers who wants to see how often this is happening for a
particular workload.

Signed-off-by: Chunguang Xu <brookxu@tencent.com>
Link: https://lore.kernel.org/r/0a165ac0-1912-aebd-8a0d-b42e7cd1aea1@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
brookxu 2020-08-15 08:10:44 +08:00 committed by Theodore Ts'o
parent 7ca4fcba92
commit c55ee7d202
1 changed files with 6 additions and 3 deletions
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9
fs/ext4/mballoc.c
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@ -2309,6 +2309,7 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
struct ext4_sb_info *sbi;
struct super_block *sb;
struct ext4_buddy e4b;
unsigned int lost;
sb = ac->ac_sb;
sbi = EXT4_SB(sb);
@ -2456,22 +2457,24 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
* We've been searching too long. Let's try to allocate
* the best chunk we've found so far
*/
ext4_mb_try_best_found(ac, &e4b);
if (ac->ac_status != AC_STATUS_FOUND) {
/*
* Someone more lucky has already allocated it.
* The only thing we can do is just take first
* found block(s)
printk(KERN_DEBUG "EXT4-fs: someone won our chunk\n");
*/
lost = (unsigned int)atomic_inc_return(&sbi->s_mb_lost_chunks);
mb_debug(sb, "lost chunk, group: %u, start: %d, len: %d, lost: %u\n",
ac->ac_b_ex.fe_group, ac->ac_b_ex.fe_start,
ac->ac_b_ex.fe_len, lost);
ac->ac_b_ex.fe_group = 0;
ac->ac_b_ex.fe_start = 0;
ac->ac_b_ex.fe_len = 0;
ac->ac_status = AC_STATUS_CONTINUE;
ac->ac_flags |= EXT4_MB_HINT_FIRST;
cr = 3;
atomic_inc(&sbi->s_mb_lost_chunks);
goto repeat;
}
}