linux-ext4 - Re: [PATCH v2 6/7] quota: simplify drop_dquot

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Date:   Thu, 29 Jun 2023 20:13:05 +0800
From:   Baokun Li <libaokun1@...wei.com>
To:     Jan Kara <jack@...e.cz>
CC:     <linux-fsdevel@...r.kernel.org>, <linux-ext4@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <yi.zhang@...wei.com>,
        <yangerkun@...wei.com>, <chengzhihao1@...wei.com>,
        <yukuai3@...wei.com>, Baokun Li <libaokun1@...wei.com>
Subject: Re: [PATCH v2 6/7] quota: simplify drop_dquot_ref()

On 2023/6/29 19:08, Jan Kara wrote:
> On Wed 28-06-23 21:21:54, Baokun Li wrote:
>> Now when dqput() drops the last reference count, it will call
>> synchronize_srcu(&dquot_srcu) in quota_release_workfn() to ensure that
>> no other user will use the dquot after the last reference count is dropped,
>> so we don't need to call synchronize_srcu(&dquot_srcu) in drop_dquot_ref()
>> and remove the corresponding logic directly to simplify the code.
> Nice simplification!  It is also important that dqput() now cannot sleep
> which was another reason for the logic with tofree_head in
> remove_inode_dquot_ref().

I don't understand this sentence very well, so I would appreciate it

if you could explain it in detail. 🤔

> Probably this is good to mention in the
> changelog.
>
>> Signed-off-by: Baokun Li <libaokun1@...wei.com>
>> ---
>>   fs/quota/dquot.c | 33 ++++++---------------------------
>>   1 file changed, 6 insertions(+), 27 deletions(-)
>>
>> diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
>> index e8e702ac64e5..df028fb2ce72 100644
>> --- a/fs/quota/dquot.c
>> +++ b/fs/quota/dquot.c
>> @@ -1090,8 +1090,7 @@ static int add_dquot_ref(struct super_block *sb, int type)
>>    * Remove references to dquots from inode and add dquot to list for freeing
>>    * if we have the last reference to dquot
>>    */
>> -static void remove_inode_dquot_ref(struct inode *inode, int type,
>> -				   struct list_head *tofree_head)
>> +static void remove_inode_dquot_ref(struct inode *inode, int type)
>>   {
>>   	struct dquot **dquots = i_dquot(inode);
>>   	struct dquot *dquot = dquots[type];
>> @@ -1100,21 +1099,7 @@ static void remove_inode_dquot_ref(struct inode *inode, int type,
>>   		return;
>>   
>>   	dquots[type] = NULL;
>> -	if (list_empty(&dquot->dq_free)) {
>> -		/*
>> -		 * The inode still has reference to dquot so it can't be in the
>> -		 * free list
>> -		 */
>> -		spin_lock(&dq_list_lock);
>> -		list_add(&dquot->dq_free, tofree_head);
>> -		spin_unlock(&dq_list_lock);
>> -	} else {
>> -		/*
>> -		 * Dquot is already in a list to put so we won't drop the last
>> -		 * reference here.
>> -		 */
>> -		dqput(dquot);
>> -	}
>> +	dqput(dquot);
>>   }
> I think you can also just drop remove_inode_dquot_ref() as it is trivial
> now and inline it at its only callsite...
>
> 								Honza
Sure, I'll just remove it in the next version and inline the only 
remaining code
into remove_dquot_ref().

Thanks!
-- 
With Best Regards,
Baokun Li
.