Commit c55ee7d2 authored by brookxu's avatar brookxu Committed by Theodore Ts'o
Browse files

ext4: add mb_debug logging when there are lost chunks 



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: default avatarChunguang Xu <brookxu@tencent.com>
Link: https://lore.kernel.org/r/0a165ac0-1912-aebd-8a0d-b42e7cd1aea1@gmail.com


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 7ca4fcba

fs/ext4/mballoc.c

+6 −3
Original line number Diff line number Diff line
@@ -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;

		}

	}