Re: [PATCH V3 4/5] ext4: get discard out of jbd2 commit kthread contex
From: "Theodore Ts'o" <tytso@mit.edu>
Date: 2021-08-12 19:47:01
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On Sat, Jul 24, 2021 at 03:41:23PM +0800, Wang Jianchao wrote:
quoted hunk ↗ jump to hunk
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 34be2f07449d..a496509e61b7 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c@@ -3474,6 +3530,14 @@ int ext4_mb_release(struct super_block *sb) struct kmem_cache *cachep = get_groupinfo_cache(sb->s_blocksize_bits); int count; + if (test_opt(sb, DISCARD)) { + /* + * wait the discard work to drain all of ext4_free_data + */ + queue_work(ext4_discard_wq, &sbi->s_discard_work); + flush_work(&sbi->s_discard_work);
I agree with Jan --- it's not clear to me why the call to queue_work() is needed. After the flush_work() call returns, if s_discard_work is still non-empty, there must be something terribly wrong --- are we missing something?
quoted hunk ↗ jump to hunk
@@ -3672,8 +3724,14 @@ int __init ext4_init_mballoc(void) if (ext4_free_data_cachep == NULL) goto out_ac_free; + ext4_discard_wq = alloc_workqueue("ext4discard", WQ_UNBOUND, 0); + if (!ext4_discard_wq) + goto out_free_data; +
Perhaps we should only allocate the workqueue when it's needed --- e.g., when a file system is mounted or remounted with "-o discard"? Then in ext4_exit_malloc(), we only free it if ext4_discard_wq is non-NULL. This would save a bit of memory on systems that wouldn't need the ext4 discard work queue. - Ted