On 2021/8/13 3:46 AM, Theodore Ts'o wrote:
> On Sat, Jul 24, 2021 at 03:41:23PM +0800, Wang Jianchao wrote:
>> 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?
Yes，the queue_work() is redundant.
I will get rid of it in next version.
>
>> @@ -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.
Yes, it make sense to the system with pool memory
Thanks so much
Jianchao
>
> - Ted
>
