2005-01-24 20:27:00

by Alex Tomas

Subject: Re: [Ext2-devel] [PATCH] JBD: log space management optimization

>>>>> Stephen C Tweedie (SCT) writes:

SCT> If you returned them to the handle directly, it would be slightly more
SCT> efficient.

good point. thanks. here is the fixed patch.


during truncate ext3 calls journal_forget() for freed blocks, but
before these blocks go to the transaction and jbd reserves space
in log for them (->t_outstanding_credits). also, journal_forget()
removes these blocks from the transaction, but doesn't correct
log space reservation. for example, removal of 500MB file reserves
136 blocks, but only 10 blocks go to the log. a commit is expensive
and correct reservation allows us to avoid needless commits. here
is the patch. tested on UP.



Signed-off-by: Alex Tomas <[email protected]>
Index: linux-2.6.7/fs/jbd/transaction.c
===================================================================
--- linux-2.6.7.orig/fs/jbd/transaction.c 2004-08-26 17:12:40.000000000 +0400
+++ linux-2.6.7/fs/jbd/transaction.c 2005-01-24 22:51:34.000000000 +0300
@@ -1204,6 +1204,7 @@
transaction_t *transaction = handle->h_transaction;
journal_t *journal = transaction->t_journal;
struct journal_head *jh;
+ int drop_reserve = 0;

BUFFER_TRACE(bh, "entry");

@@ -1227,6 +1228,7 @@
J_ASSERT_JH(jh, !jh->b_committed_data);

__journal_unfile_buffer(jh);
+ drop_reserve = 1;

/*
* We are no longer going to journal this buffer.
@@ -1249,7 +1251,7 @@
spin_unlock(&journal->j_list_lock);
jbd_unlock_bh_state(bh);
__bforget(bh);
- return;
+ goto drop;
}
}
} else if (jh->b_transaction) {
@@ -1264,6 +1266,7 @@
if (jh->b_next_transaction) {
J_ASSERT(jh->b_next_transaction == transaction);
jh->b_next_transaction = NULL;
+ drop_reserve = 1;
}
}

@@ -1271,6 +1274,13 @@
spin_unlock(&journal->j_list_lock);
jbd_unlock_bh_state(bh);
__brelse(bh);
+
+drop:
+ if (drop_reserve) {
+ /* no need to reserve log space for this block -bzzz */
+ handle->h_buffer_credits++;
+ }
+
return;
}

2005-01-24 21:03:26

by Stephen C. Tweedie

Subject: Re: [Ext2-devel] [PATCH] JBD: log space management optimization

Hi,

On Mon, 2005-01-24 at 20:22, Alex Tomas wrote:

> during truncate ext3 calls journal_forget() for freed blocks, but
> before these blocks go to the transaction and jbd reserves space
> in log for them (->t_outstanding_credits). also, journal_forget()
> removes these blocks from the transaction, but doesn't correct
> log space reservation. for example, removal of 500MB file reserves
> 136 blocks, but only 10 blocks go to the log. a commit is expensive
> and correct reservation allows us to avoid needless commits. here
> is the patch. tested on UP.

> +drop:
> + if (drop_reserve) {
> + /* no need to reserve log space for this block -bzzz */
> + handle->h_buffer_credits++;
> + }
> +

Looks good to me.

--Stephen