linux-kernel - Re: [PATCH v2 2/7] quota: add new global dquot list releasing

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Message-ID: <e2b328fa-f5ed-c1ec-2b20-60ed53c9b8a7@huawei.com>
Date:   Thu, 29 Jun 2023 19:10:47 +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 2/7] quota: add new global dquot list releasing_dquots

On 2023/6/29 18:29, Jan Kara wrote:
> On Wed 28-06-23 21:21:50, Baokun Li wrote:
>> Add a new global dquot list that obeys the following rules:
>>
>>   1). A dquot is added to this list when its last reference count is about
>>       to be dropped.
>>   2). The reference count of the dquot in the list is greater than or equal
>>       to 1 ( due to possible race with dqget()).
>>   3). When a dquot is removed from this list, a reference count is always
>>       subtracted, and if the reference count is then 0, the dquot is added
>>       to the free_dquots list.
>>
>> This list is used to safely perform the final cleanup before releasing
>> the last reference count, to avoid various contention issues caused by
>> performing cleanup directly in dqput(), and to avoid the performance impact
>> caused by calling synchronize_srcu(&dquot_srcu) directly in dqput(). Here
>> it is just defining the list and implementing the corresponding operation
>> function, which we will use later.
>>
>> Suggested-by: Jan Kara <jack@...e.cz>
>> Signed-off-by: Baokun Li <libaokun1@...wei.com>
> I think you can merge this patch with patch 5. It is not like separating
> this bit helps in review or anything...
OK, I just don't want to cram a lot of stuff into patch 5, I will merge 
this patch
into patch 5 in the next version.
>> diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
>> index 108ba9f1e420..a8b43b5b5623 100644
>> --- a/fs/quota/dquot.c
>> +++ b/fs/quota/dquot.c
>> @@ -226,12 +226,21 @@ static void put_quota_format(struct quota_format_type *fmt)
>>   /*
>>    * Dquot List Management:
>>    * The quota code uses four lists for dquot management: the inuse_list,
>                            ^^^ five now :)
Yes, indeed, I forgot to correct here.
>
>> - * free_dquots, dqi_dirty_list, and dquot_hash[] array. A single dquot
>> - * structure may be on some of those lists, depending on its current state.
>> + * releasing_dquots, free_dquots, dqi_dirty_list, and dquot_hash[] array.
>> + * A single dquot structure may be on some of those lists, depending on
>> + * its current state.
>>    *
>>    * All dquots are placed to the end of inuse_list when first created, and this
>>    * list is used for invalidate operation, which must look at every dquot.
>>    *
>> + * When the last reference of a dquot will be dropped, the dquot will be
>> + * added to releasing_dquots. We'd then queue work item which would call
>> + * synchronize_srcu() and after that perform the final cleanup of all the
>> + * dquots on the list. Both releasing_dquots and free_dquots use the
>> + * dq_free list_head in the dquot struct. when a dquot is removed from
> 					     ^^^ Capital W please
Good catch！Very sorry for the oversight here.
>> + * releasing_dquots, a reference count is always subtracted, and if
>> + * dq_count == 0 at that point, the dquot will be added to the free_dquots.
>> + *
> 								Honza
Thank you very much for your careful REVIEW! I will fix those in the 
next version!

-- 
With Best Regards,
Baokun Li
.