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Message-ID: <20081009030054.GD17512@mit.edu>
Date: Wed, 8 Oct 2008 23:00:54 -0400
From: Theodore Tso <tytso@....edu>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Arjan van de Ven <arjan@...radead.org>,
Jens Axboe <jens.axboe@...cle.com>,
linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
linux-ext4@...r.kernel.org
Subject: Re: [PATCH] Give kjournald a IOPRIO_CLASS_RT io priority
On Thu, Oct 02, 2008 at 10:24:38PM -0700, Andrew Morton wrote:
>
> Mount a junk partition with `-oakpm' and run some benchmarks. If the
> results are "wow" then it's worth spending time on. If the results are
> "meh" then we can not bother..
>
I've ported the patch to the ext4 filesystem, and dropped it into the
unstable portion of the ext4 patch queue. If we can get someone (hi,
Ric!) to run fs_mark with and without -o akpm_lock_hack, I suspect we
will find that it makes quite a large difference on that particular
benchmark, since it is fsync-heavy to force a large number of
transaction, and the creation of the inodes should cause multiple
blocks that will be entangled between the current and committing
transactions.
- Ted
ext4: akpm's locking hack to fix locking delays
This is a port of the following patch from Andrew Morton to ext4:
http://lkml.org/lkml/2008/10/3/22
This fixes a major contention problem in do_get_write_access() when a
buffer is modified in both the current and committing transaction.
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
Cc: akpm@...ux-foundation.org
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index f46a513..23822fb 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -540,6 +540,7 @@ do { \
#define EXT4_MOUNT_JOURNAL_ASYNC_COMMIT 0x1000000 /* Journal Async Commit */
#define EXT4_MOUNT_I_VERSION 0x2000000 /* i_version support */
#define EXT4_MOUNT_DELALLOC 0x8000000 /* Delalloc support */
+#define EXT4_MOUNT_AKPM_LOCK_HACK 0x10000000 /* akpm lock hack */
/* Compatibility, for having both ext2_fs.h and ext4_fs.h included at once */
#ifndef _LINUX_EXT2_FS_H
#define clear_opt(o, opt) o &= ~EXT4_MOUNT_##opt
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 67ebefb..f4e7157 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -752,6 +752,8 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
seq_puts(seq, ",journal_async_commit");
if (test_opt(sb, NOBH))
seq_puts(seq, ",nobh");
+ if (test_opt(sb, AKPM_LOCK_HACK))
+ seq_puts(seq, ",akpm_lock_hack");
if (!test_opt(sb, EXTENTS))
seq_puts(seq, ",noextents");
if (test_opt(sb, I_VERSION))
@@ -911,7 +913,7 @@ enum {
Opt_ignore, Opt_barrier, Opt_err, Opt_resize, Opt_usrquota,
Opt_grpquota, Opt_extents, Opt_noextents, Opt_i_version,
Opt_mballoc, Opt_nomballoc, Opt_stripe, Opt_delalloc, Opt_nodelalloc,
- Opt_inode_readahead_blks
+ Opt_inode_readahead_blks, Opt_akpm_lock_hack,
};
static match_table_t tokens = {
@@ -973,6 +975,7 @@ static match_table_t tokens = {
{Opt_delalloc, "delalloc"},
{Opt_nodelalloc, "nodelalloc"},
{Opt_inode_readahead_blks, "inode_readahead_blks=%u"},
+ {Opt_akpm_lock_hack, "akpm_lock_hack"},
{Opt_err, NULL},
};
@@ -1382,6 +1385,9 @@ set_qf_format:
return 0;
sbi->s_inode_readahead_blks = option;
break;
+ case Opt_akpm_lock_hack:
+ set_opt(sbi->s_mount_opt, AKPM_LOCK_HACK);
+ break;
default:
printk(KERN_ERR
"EXT4-fs: Unrecognized mount option \"%s\" "
@@ -2534,6 +2540,10 @@ static void ext4_init_journal_params(struct super_block *sb, journal_t *journal)
journal->j_flags |= JBD2_BARRIER;
else
journal->j_flags &= ~JBD2_BARRIER;
+ if (test_opt(sb, AKPM_LOCK_HACK))
+ journal->j_flags |= JBD2_LOCK_HACK;
+ else
+ journal->j_flags &= ~JBD2_LOCK_HACK;
spin_unlock(&journal->j_state_lock);
}
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index e5d5405..32c288a 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -546,6 +546,7 @@ do_get_write_access(handle_t *handle, struct journal_head *jh,
int error;
char *frozen_buffer = NULL;
int need_copy = 0;
+ int locked = 0;
if (is_handle_aborted(handle))
return -EROFS;
@@ -561,7 +562,13 @@ repeat:
/* @@@ Need to check for errors here at some point. */
- lock_buffer(bh);
+ if (journal->j_flags & JBD2_LOCK_HACK) {
+ if (trylock_buffer(bh))
+ locked = 1; /* lolz */
+ } else {
+ lock_buffer(bh);
+ locked = 1;
+ }
jbd_lock_bh_state(bh);
/* We now hold the buffer lock so it is safe to query the buffer
@@ -600,7 +607,8 @@ repeat:
jbd_unexpected_dirty_buffer(jh);
}
- unlock_buffer(bh);
+ if (locked)
+ unlock_buffer(bh);
error = -EROFS;
if (is_handle_aborted(handle)) {
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 66c3499..c614dae 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -967,6 +967,7 @@ struct journal_s
#define JBD2_FLUSHED 0x008 /* The journal superblock has been flushed */
#define JBD2_LOADED 0x010 /* The journal superblock has been loaded */
#define JBD2_BARRIER 0x020 /* Use IDE barriers */
+#define JBD2_LOCK_HACK 0x040 /* akpm's locking hack */
/*
* Function declarations for the journaling transaction and buffer
--
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