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

Jan Kara
2011-11-14T15:36:19Z

On Mon 14-11-11 07:22:03, Manish Katiyar wrote:
> On Mon, Nov 14, 2011 at 4:53 AM, Jan Kara <jack@suse.cz> wrote:
> > 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
>
> I had submitted a similar patch for ext3, but it was rejected by
> Andrew Morton. http://lists.openwall.net/linux-ext4/2011/06/13/15
Now I remember :) Anyway, "it makes debugging simpler" is really the
reason which would change Andrew's mind I guess. I actually used a patch
like this once or twice exactly to debug some stuff... That's why I think
the patch has a value for ext4/jbd2 and I'll follow their lead with ext3.

Honza

> > 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
> > --
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> >
>
>
>
> --
> Thanks -
> Manish
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
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