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Message-Id: <20081002222438.8f9f90a2.akpm@linux-foundation.org>
Date: Thu, 2 Oct 2008 22:24:38 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Arjan van de Ven <arjan@...radead.org>
Cc: Jens Axboe <jens.axboe@...cle.com>, linux-kernel@...r.kernel.org,
Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] Give kjournald a IOPRIO_CLASS_RT io priority
On Thu, 2 Oct 2008 22:00:40 -0700 Arjan van de Ven <arjan@...radead.org> wrote:
> > Of course, fixing this running-vs-committing contention point would
> > fix a lot more things than just atime updates.
>
> yes clearly. It's waaay above my paygrade to hack on though; JBD is one
> of those places in the kernel that scare me for doing fundamental
> changes ;-(
If someone has an hour or so to kill, we can pretend to fix it:
fs/ext3/super.c | 12 +++++++++++-
fs/jbd/transaction.c | 13 +++++++++++--
include/linux/ext3_fs.h | 1 +
include/linux/jbd.h | 1 +
4 files changed, 24 insertions(+), 3 deletions(-)
diff -puN fs/ext3/super.c~a fs/ext3/super.c
--- a/fs/ext3/super.c~a
+++ a/fs/ext3/super.c
@@ -617,6 +617,8 @@ static int ext3_show_options(struct seq_
seq_puts(seq, ",barrier=1");
if (test_opt(sb, NOBH))
seq_puts(seq, ",nobh");
+ if (test_opt(sb, AKPM))
+ seq_puts(seq, ",akpm");
if (test_opt(sb, DATA_FLAGS) == EXT3_MOUNT_JOURNAL_DATA)
seq_puts(seq, ",data=journal");
@@ -757,7 +759,7 @@ enum {
Opt_usrjquota, Opt_grpjquota, Opt_offusrjquota, Opt_offgrpjquota,
Opt_jqfmt_vfsold, Opt_jqfmt_vfsv0, Opt_quota, Opt_noquota,
Opt_ignore, Opt_barrier, Opt_err, Opt_resize, Opt_usrquota,
- Opt_grpquota
+ Opt_grpquota, Opt_akpm,
};
static match_table_t tokens = {
@@ -808,6 +810,7 @@ static match_table_t tokens = {
{Opt_usrquota, "usrquota"},
{Opt_barrier, "barrier=%u"},
{Opt_resize, "resize"},
+ {Opt_akpm, "akpm"},
{Opt_err, NULL},
};
@@ -1097,6 +1100,9 @@ set_qf_format:
set_opt(sbi->s_mount_opt, QUOTA);
set_opt(sbi->s_mount_opt, GRPQUOTA);
break;
+ case Opt_akpm:
+ set_opt(sbi->s_mount_opt, AKPM);
+ break;
case Opt_noquota:
if (sb_any_quota_enabled(sb) ||
sb_any_quota_suspended(sb)) {
@@ -1986,6 +1992,10 @@ static void ext3_init_journal_params(str
journal->j_flags |= JFS_BARRIER;
else
journal->j_flags &= ~JFS_BARRIER;
+ if (test_opt(sb, AKPM))
+ journal->j_flags |= JFS_AKPM;
+ else
+ journal->j_flags &= ~JFS_AKPM;
spin_unlock(&journal->j_state_lock);
}
diff -puN include/linux/ext3_fs.h~a include/linux/ext3_fs.h
--- a/include/linux/ext3_fs.h~a
+++ a/include/linux/ext3_fs.h
@@ -380,6 +380,7 @@ struct ext3_inode {
#define EXT3_MOUNT_QUOTA 0x80000 /* Some quota option set */
#define EXT3_MOUNT_USRQUOTA 0x100000 /* "old" user quota */
#define EXT3_MOUNT_GRPQUOTA 0x200000 /* "old" group quota */
+#define EXT3_MOUNT_AKPM 0x400000
/* Compatibility, for having both ext2_fs.h and ext3_fs.h included at once */
#ifndef _LINUX_EXT2_FS_H
diff -puN include/linux/jbd.h~a include/linux/jbd.h
--- a/include/linux/jbd.h~a
+++ a/include/linux/jbd.h
@@ -816,6 +816,7 @@ struct journal_s
#define JFS_FLUSHED 0x008 /* The journal superblock has been flushed */
#define JFS_LOADED 0x010 /* The journal superblock has been loaded */
#define JFS_BARRIER 0x020 /* Use IDE barriers */
+#define JFS_AKPM 0x040
/*
* Function declarations for the journaling transaction and buffer
diff -puN fs/jbd/transaction.c~a fs/jbd/transaction.c
--- a/fs/jbd/transaction.c~a
+++ a/fs/jbd/transaction.c
@@ -537,6 +537,7 @@ do_get_write_access(handle_t *handle, st
int error;
char *frozen_buffer = NULL;
int need_copy = 0;
+ int locked;
if (is_handle_aborted(handle))
return -EROFS;
@@ -552,7 +553,14 @@ repeat:
/* @@@ Need to check for errors here at some point. */
- lock_buffer(bh);
+ locked = 0;
+ if (journal->j_flags & JFS_AKPM) {
+ 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
@@ -591,7 +599,8 @@ repeat:
jbd_unexpected_dirty_buffer(jh);
}
- unlock_buffer(bh);
+ if (locked)
+ unlock_buffer(bh);
error = -EROFS;
if (is_handle_aborted(handle)) {
_
(might emit nasty warnings or assertion failures which will need to be
disabled)
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..
--
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