linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Wang Jianchao <jianchao.wan9@gmail.com>
To: Jan Kara <jack@suse.cz>
Cc: linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org,
	tytso@mit.edu, adilger.kernel@dilger.ca
Subject: Re: [PATCH V3 4/5] ext4: get discard out of jbd2 commit kthread contex
Date: Thu, 26 Aug 2021 15:15:55 +0800	[thread overview]
Message-ID: <6621227f-e710-2fa2-bc09-c4c66c34eb14@gmail.com> (raw)
In-Reply-To: <20210804154530.GL4578@quack2.suse.cz>



On 2021/8/4 11:45 PM, Jan Kara wrote:
> On Sat 24-07-21 15:41:23, Wang Jianchao wrote:
>> From: Wang Jianchao <wangjianchao@kuaishou.com>
>>
>> Right now, discard is issued and waited to be completed in jbd2
>> commit kthread context after the logs are committed. When large
>> amount of files are deleted and discard is flooding, jbd2 commit
>> kthread can be blocked for long time. Then all of the metadata
>> operations can be blocked to wait the log space.
>>
>> One case is the page fault path with read mm->mmap_sem held, which
>> wants to update the file time but has to wait for the log space.
>> When other threads in the task wants to do mmap, then write mmap_sem
>> is blocked. Finally all of the following read mmap_sem requirements
>> are blocked, even the ps command which need to read the /proc/pid/
>> -cmdline. Our monitor service which needs to read /proc/pid/cmdline
>> used to be blocked for 5 mins.
>>
>> This patch frees the blocks back to buddy after commit and then do
>> discard in a async kworker context in fstrim fashion, namely,
>>  - mark blocks to be discarded as used if they have not been allocated
>>  - do discard
>>  - mark them free
>> After this, jbd2 commit kthread won't be blocked any more by discard
>> and we won't get NOSPC even if the discard is slow or throttled.
>>
>> Link: https://marc.info/?l=linux-kernel&m=162143690731901&w=2
>> Suggested-by: Theodore Ts'o <tytso@mit.edu>
>> Signed-off-by: Wang Jianchao <wangjianchao@kuaishou.com>
> 
> Looks good to me. Just one small comment below. With that addressed feel
> free to add:
> 
> Reviewed-by: Jan Kara <jack@suse.cz>
> 
> 
>> @@ -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);
> 
> Do we really need to queue the work here? The filesystem should be
> quiescent by now, we take care to queue the work whenever we add item to
> empty list. So it should be enough to have flush_work() here and then
> possibly
> 
> 	WARN_ON_ONCE(!list_empty(&sbi->s_discard_list))
> 
> Or am I missing something?

queue_work here is indeed redundant.

Thanks so much for you point out this.
Jianchao

> 
> 								Honza
> 
>> +		flush_work(&sbi->s_discard_work);
>> +	}
>> +

  reply	other threads:[~2021-08-26  7:16 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-24  7:41 [PATCH V3 0/5] ext4: get discard out of jbd2 commit context Wang Jianchao
2021-07-24  7:41 ` [PATCH V3 1/5] ext4: remove the 'group' parameter of ext4_trim_extent Wang Jianchao
2021-07-26  3:42   ` Guoqing Jiang
2021-08-04 15:26   ` Jan Kara
2021-07-24  7:41 ` [PATCH V3 2/5] ext4: add new helper interface ext4_try_to_trim_range() Wang Jianchao
2021-08-04 15:29   ` Jan Kara
2021-08-12 17:44   ` Theodore Ts'o
2021-08-26  7:19     ` Wang Jianchao
2021-07-24  7:41 ` [PATCH V3 3/5] ext4: remove the repeated comment of ext4_trim_all_free Wang Jianchao
2021-08-04 15:27   ` Jan Kara
2021-07-24  7:41 ` [PATCH V3 4/5] ext4: get discard out of jbd2 commit kthread contex Wang Jianchao
2021-08-04 15:45   ` Jan Kara
2021-08-26  7:15     ` Wang Jianchao [this message]
2021-08-12 19:46   ` Theodore Ts'o
2021-08-26  7:51     ` Wang Jianchao
2021-08-26  8:58       ` Wang Jianchao
2021-07-24  7:41 ` [PATCH V3 5/5] ext4: make fallocate retry when err is ENOSPC Wang Jianchao
2021-07-26  3:40   ` Guoqing Jiang
2021-07-26  7:05     ` Wang Jianchao
2021-08-04 15:52       ` Jan Kara
2021-08-26 11:42         ` Wang Jianchao
2021-08-04 15:32   ` Jan Kara
2021-08-04 15:46     ` Jan Kara

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=6621227f-e710-2fa2-bc09-c4c66c34eb14@gmail.com \
    --to=jianchao.wan9@gmail.com \
    --cc=adilger.kernel@dilger.ca \
    --cc=jack@suse.cz \
    --cc=linux-ext4@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=tytso@mit.edu \
    --subject='Re: [PATCH V3 4/5] ext4: get discard out of jbd2 commit kthread contex' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).