linux-ext4 - Re: [PATCH v2 2/7] quota: add new global dquot list releasing

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Message-ID: <20230629102952.ifn3qdoh632ybsb5@quack3>
Date:   Thu, 29 Jun 2023 12:29:52 +0200
From:   Jan Kara <jack@...e.cz>
To:     Baokun Li <libaokun1@...wei.com>
Cc:     jack@...e.cz, 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
Subject: Re: [PATCH v2 2/7] quota: add new global dquot list releasing_dquots

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...

> 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 :)

> - * 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

> + * 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
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR