linux-ext4 - Re: [PATCH] jbd2: Avoid long replay times due to high number or revoke blocks

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Message-ID: <6c9ce6fe-9d6f-49cf-b274-3355bb1ea8af@huawei.com>
Date: Fri, 17 Jan 2025 10:58:42 +0800
From: Zhang Yi <yi.zhang@...wei.com>
To: Jan Kara <jack@...e.cz>
CC: <linux-ext4@...r.kernel.org>, Andreas Dilger <adilger@...ger.ca>, Alexey
 Zhuravlev <azhuravlev@....com>, Ted Tso <tytso@....edu>
Subject: Re: [PATCH] jbd2: Avoid long replay times due to high number or
 revoke blocks

On 2025/1/17 2:02, Jan Kara wrote:
> Some users are reporting journal replay takes a long time when there is
> excessive number of revoke blocks in the journal. Reported times are
> like:
> 
> 1048576 records - 95 seconds
> 2097152 records - 580 seconds
> 
> The problem is that hash chains in the revoke table gets excessively
> long in these cases. Fix the problem by sizing the revoke table
> appropriately before the revoke pass.
> 
> Thanks to Alexey Zhuravlev <azhuravlev@....com> for benchmarking the patch with
> large numbers of revoke blocks [1].
> 
> [1] https://lore.kernel.org/all/20250113183107.7bfef7b6@x390.bzzz77.ru
> 
> Signed-off-by: Jan Kara <jack@...e.cz>

Hi, Jan,

This overall patch looks good to me; however, it appears to be not
based on the latested version of the upstream kernel, and I have one
minor suggestion below.

> ---
>  fs/jbd2/recovery.c   | 54 +++++++++++++++++++++++++++++++++++++-------
>  fs/jbd2/revoke.c     |  8 +++----
>  include/linux/jbd2.h |  2 ++
>  3 files changed, 52 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/jbd2/recovery.c b/fs/jbd2/recovery.c
> index 667f67342c52..9845f72e456a 100644
> --- a/fs/jbd2/recovery.c
> +++ b/fs/jbd2/recovery.c
> @@ -39,7 +39,7 @@ struct recovery_info
>  
>  static int do_one_pass(journal_t *journal,
>  				struct recovery_info *info, enum passtype pass);
> -static int scan_revoke_records(journal_t *, struct buffer_head *,
> +static int scan_revoke_records(journal_t *, enum passtype, struct buffer_head *,
>  				tid_t, struct recovery_info *);
>  
>  #ifdef __KERNEL__
> @@ -327,6 +327,12 @@ int jbd2_journal_recover(journal_t *journal)
>  		  journal->j_transaction_sequence, journal->j_head);
>  
>  	jbd2_journal_clear_revoke(journal);
> +	/* Free revoke table allocated for replay */
> +	if (journal->j_revoke != journal->j_revoke_table[0] &&
> +	    journal->j_revoke != journal->j_revoke_table[1]) {
> +		jbd2_journal_destroy_revoke_table(journal->j_revoke);
> +		journal->j_revoke = journal->j_revoke_table[1];
> +	}
>  	err2 = sync_blockdev(journal->j_fs_dev);
>  	if (!err)
>  		err = err2;
> @@ -517,6 +523,31 @@ static int do_one_pass(journal_t *journal,
>  	first_commit_ID = next_commit_ID;
>  	if (pass == PASS_SCAN)
>  		info->start_transaction = first_commit_ID;
> +	else if (pass == PASS_REVOKE) {
> +		/*
> +		 * Would the default revoke table have too long hash chains
> +		 * during replay?
> +		 */
> +		if (info->nr_revokes > JOURNAL_REVOKE_DEFAULT_HASH * 16) {
> +			unsigned int hash_size;
> +
> +			/*
> +			 * Aim for average chain length of 8, limit at 1M
> +			 * entries to avoid problems with malicious
> +			 * filesystems.
> +			 */
> +			hash_size = min(roundup_pow_of_two(info->nr_revokes / 8),
> +					1U << 20);
> +			journal->j_revoke =
> +				jbd2_journal_init_revoke_table(hash_size);
> +			if (!journal->j_revoke) {
> +				printk(KERN_ERR
> +				       "JBD2: failed to allocate revoke table for replay with %u entries. "
> +				       "Journal replay may be slow.\n", hash_size);
> +				journal->j_revoke = journal->j_revoke_table[1];
> +			}
> +		}
> +	}
>  
>  	jbd2_debug(1, "Starting recovery pass %d\n", pass);
>  
> @@ -874,14 +905,16 @@ static int do_one_pass(journal_t *journal,
>  				need_check_commit_time = true;
>  			}
>  
> -			/* If we aren't in the REVOKE pass, then we can
> -			 * just skip over this block. */
> -			if (pass != PASS_REVOKE) {
> +			/*
> +			 * If we aren't in the SCAN or REVOKE pass, then we can
> +			 * just skip over this block.
> +			 */
> +			if (pass != PASS_REVOKE && pass != PASS_SCAN) {
>  				brelse(bh);
>  				continue;
>  			}

How about move this code snippets to the beginning of the
JBD2_REVOKE_BLOCK branch case?

Thanks,
Yi.


>  
>  extern void	   jbd2_journal_destroy_revoke(journal_t *);
>  extern int	   jbd2_journal_revoke (handle_t *, unsigned long long, struct buffer_head *);