Re: [PATCH 1/2] jbd: allocate transacion from special cache

[Jan Kara <jack@suse.cz>]

On Sun 13-11-11 19:29:31, Yongqiang Yang wrote:
> transaction_t is 100 bytes under 32-bit systems. Transactions
> allocated from general cache comsume 128 bytes. This patch
> lets jbd allocates transacion from special cache.
> 
> Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
  Space saving isn't probably a good argument here since the number of
transactions on the system is going to be rather low (a couple per ext3
filesystem). The reason why I wanted this change for JBD2 is that it makes
debugging of memory corruption of a transaction structure much easier (and
I've been tracking down issues like this several times already).

That being said, I don't find strong need to have this in ext3 and thus
I'll take the change in jbd/ext3 if Ted takes the similar change to
jbd2/ext4 to keep compatibility. Manish Katiyar was working on it
(http://comments.gmane.org/gmane.comp.file-systems.ext4/25884) but it seems
it wasn't merged yet.

									Honza

> ---
>  fs/jbd/checkpoint.c  |    2 +-
>  fs/jbd/journal.c     |    3 +++
>  fs/jbd/transaction.c |   31 +++++++++++++++++++++++++++++--
>  include/linux/jbd.h  |    5 +++++
>  4 files changed, 38 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/jbd/checkpoint.c b/fs/jbd/checkpoint.c
> index f94fc48..4d98046 100644
> --- a/fs/jbd/checkpoint.c
> +++ b/fs/jbd/checkpoint.c
> @@ -764,5 +764,5 @@ void __journal_drop_transaction(journal_t *journal, transaction_t *transaction)
>  
>  	trace_jbd_drop_transaction(journal, transaction);
>  	jbd_debug(1, "Dropping transaction %d, all done\n", transaction->t_tid);
> -	kfree(transaction);
> +	journal_free_transaction(transaction);
>  }
> diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
> index 9fe061f..45ca982 100644
> --- a/fs/jbd/journal.c
> +++ b/fs/jbd/journal.c
> @@ -2004,6 +2004,8 @@ static int __init journal_init_caches(void)
>  		ret = journal_init_journal_head_cache();
>  	if (ret == 0)
>  		ret = journal_init_handle_cache();
> +	if (ret == 0)
> +		ret = journal_init_transaction_cache();
>  	return ret;
>  }
>  
> @@ -2012,6 +2014,7 @@ static void journal_destroy_caches(void)
>  	journal_destroy_revoke_caches();
>  	journal_destroy_journal_head_cache();
>  	journal_destroy_handle_cache();
> +	journal_destroy_transaction_cache();
>  }
>  
>  static int __init journal_init(void)
> diff --git a/fs/jbd/transaction.c b/fs/jbd/transaction.c
> index 7e59c6e..20d76f1 100644
> --- a/fs/jbd/transaction.c
> +++ b/fs/jbd/transaction.c
> @@ -30,6 +30,32 @@
>  
>  static void __journal_temp_unlink_buffer(struct journal_head *jh);
>  
> +static struct kmem_cache *transaction_cache;
> +int __init journal_init_transaction_cache(void)
> +{
> +	J_ASSERT(!transaction_cache);
> +	transaction_cache = KMEM_CACHE(transaction_s,
> +				       SLAB_HWCACHE_ALIGN|SLAB_TEMPORARY);
> +	if (transaction_cache)
> +		return 0;
> +	return -ENOMEM;
> +}
> +
> +void __init journal_destroy_transaction_cache(void)
> +{
> +	if (transaction_cache) {
> +		kmem_cache_destroy(transaction_cache);
> +		transaction_cache = NULL;
> +	}
> +}
> +
> +void journal_free_transaction(transaction_t *transaction)
> +{
> +	if (unlikely(ZERO_OR_NULL_PTR(transaction)))
> +		return;
> +	kmem_cache_free(transaction_cache, transaction);
> +}
> +
>  /*
>   * get_transaction: obtain a new transaction_t object.
>   *
> @@ -100,11 +126,12 @@ static int start_this_handle(journal_t *journal, handle_t *handle)
>  
>  alloc_transaction:
>  	if (!journal->j_running_transaction) {
> -		new_transaction = kzalloc(sizeof(*new_transaction), GFP_NOFS);
> +		new_transaction = kmem_cache_alloc(transaction_cache, GFP_NOFS);
>  		if (!new_transaction) {
>  			congestion_wait(BLK_RW_ASYNC, HZ/50);
>  			goto alloc_transaction;
>  		}
> +		memset(new_transaction, 0, sizeof(*new_transaction));
>  	}
>  
>  	jbd_debug(3, "New handle %p going live.\n", handle);
> @@ -233,7 +260,7 @@ repeat_locked:
>  	lock_map_acquire(&handle->h_lockdep_map);
>  out:
>  	if (unlikely(new_transaction))		/* It's usually NULL */
> -		kfree(new_transaction);
> +		journal_free_transaction(new_transaction);
>  	return ret;
>  }
>  
> diff --git a/include/linux/jbd.h b/include/linux/jbd.h
> index c7acdde..0f9f0b6 100644
> --- a/include/linux/jbd.h
> +++ b/include/linux/jbd.h
> @@ -807,6 +807,11 @@ journal_write_metadata_buffer(transaction_t	  *transaction,
>  /* Transaction locking */
>  extern void		__wait_on_journal (journal_t *);
>  
> +/* Transaction cache support */
> +extern void journal_destroy_transaction_cache(void);
> +extern int  journal_init_transaction_cache(void);
> +extern void journal_free_transaction(transaction_t *);
> +
>  /*
>   * Journal locking.
>   *
> -- 
> 1.7.5.1
> 
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR