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Date:   Thu, 31 Oct 2019 17:59:05 +0100
From:   Jan Kara <jack@...e.cz>
To:     Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org, jack@...e.cz, tytso@....edu,
        lixi@....com, Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Subject: Re: [PATCH] fs/ext4: get project quota from inode for mangling
 statfs results

On Thu 31-10-19 11:03:48, Dmitry Monakhov wrote:
> From: Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
> 
> Right now ext4_statfs_project() does quota lookup by id every time.
> This is costly operation, especially if there is no inode who hold
> reference to this dquot. This means that each statfs performs useless
> ext4_acquire_dquot()/ext4_release_dquot() which serialized on __jbd2_log_wait_for_space()
> dqget()
>  ->ext4_acquire_dquot
>    -> ext4_journal_start
>       -> __jbd2_log_wait_for_space
> dqput()
>   -> ext4_release_dquot
>      ->ext4_journal_start
>        ->__jbd2_log_wait_for_space
> 
> 
> Function ext4_statfs_project() could be moved into generic quota code,
> it is required for every filesystem which uses generic project quota.
> 
> Reported-by: Dmitry Monakhov <dmtrmonakhov@...dex-team.ru>
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>

Thanks! The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza


> ---
>  fs/ext4/super.c | 25 ++++++++++++++++---------
>  1 file changed, 16 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 2318e5f..4e8f97d68 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -5532,18 +5532,23 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
>  }
>  
>  #ifdef CONFIG_QUOTA
> -static int ext4_statfs_project(struct super_block *sb,
> -			       kprojid_t projid, struct kstatfs *buf)
> +static int ext4_statfs_project(struct inode *inode, struct kstatfs *buf)
>  {
> -	struct kqid qid;
> +	struct super_block *sb = inode->i_sb;
>  	struct dquot *dquot;
>  	u64 limit;
>  	u64 curblock;
> +	int err;
> +
> +	err = dquot_initialize(inode);
> +	if (err)
> +		return err;
> +
> +	spin_lock(&inode->i_lock);
> +	dquot = ext4_get_dquots(inode)[PRJQUOTA];
> +	if (!dquot)
> +		goto out_unlock;
>  
> -	qid = make_kqid_projid(projid);
> -	dquot = dqget(sb, qid);
> -	if (IS_ERR(dquot))
> -		return PTR_ERR(dquot);
>  	spin_lock(&dquot->dq_dqb_lock);
>  
>  	limit = (dquot->dq_dqb.dqb_bsoftlimit ?
> @@ -5569,7 +5574,9 @@ static int ext4_statfs_project(struct super_block *sb,
>  	}
>  
>  	spin_unlock(&dquot->dq_dqb_lock);
> -	dqput(dquot);
> +out_unlock:
> +	spin_unlock(&inode->i_lock);
> +
>  	return 0;
>  }
>  #endif
> @@ -5609,7 +5616,7 @@ static int ext4_statfs(struct dentry *dentry, struct kstatfs *buf)
>  #ifdef CONFIG_QUOTA
>  	if (ext4_test_inode_flag(dentry->d_inode, EXT4_INODE_PROJINHERIT) &&
>  	    sb_has_quota_limits_enabled(sb, PRJQUOTA))
> -		ext4_statfs_project(sb, EXT4_I(dentry->d_inode)->i_projid, buf);
> +		ext4_statfs_project(dentry->d_inode, buf);
>  #endif
>  	return 0;
>  }
> -- 
> 2.7.4
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

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