[PATCHv7 0/5] ext4: stop using write_supers and s_dirt

[PATCHv7 0/5] ext4: stop using write_supers and s_dirt

[Artem Bityutskiy]

This patch-set makes ext4 file-system stop using the VFS '->write_supers()'
call-back and the '->s_dirt' superblock field because I plan to remove them
once all users are gone.

What we do in this patch-set is we notice that ext4 does not really needed the
'write_super()' functionality and we can remove it. Instead, we simply mark the
superblock buffer as dirty directly, rather than postponing this till the next
'sync_supers()' kernel thread wake-up. Most of the ext4 changes were done or
suggested by Jan Kara - thanks Jan!

V7 is identical to v6, but I've added Jan's "Reviewed-by" and removed my
worries about slowing down the deletion path - they were false, apologies. So
only the commit messages changed.

Tested with xfstests (both journalled and non-journalled ext4 modes).

fs/ext4/ext4.h      |    9 ---------
fs/ext4/ext4_jbd2.c |    8 +++-----
fs/ext4/ext4_jbd2.h |    7 ++-----
fs/ext4/file.c      |   14 +++++++++++++-
fs/ext4/ialloc.c    |    2 --
fs/ext4/inode.c     |    2 +-
fs/ext4/mballoc.c   |    2 --
fs/ext4/namei.c     |    4 ++--
fs/ext4/resize.c    |    2 +-
fs/ext4/super.c     |   12 +-----------
10 files changed, 23 insertions(+), 39 deletions(-)

Reminder
========

The goal is to get rid of the 'sync_supers()' kernel thread. This kernel thread
wakes up every 5 seconds (by default) and calls '->write_super()' for all
mounted file-systems. And the bad thing is that this is done even if all the
superblocks are clean. Moreover, many file-systems do not even need this and
they do not even register the '->write_super()' method at all (e.g., btrfs).

So 'sync_supers()' mostly just generates useless wake-ups and wastes power.
I am trying to make all file-systems independent of '->write_super()' and plan
to remove 'sync_supers()' and '->write_super()' completely once there are no
more users.

Overall status
==============

1.  ext4: patches submitted,
    https://lkml.org/lkml/2012/7/10/195
2.  exofs: patch submitted,
    https://lkml.org/lkml/2012/6/4/211
3.  sysv: patches submitted,
    http://lkml.org/lkml/2012/7/3/250
4.  udf: patch submitted, sits in Jan Kara's tree:
    https://lkml.org/lkml/2012/6/4/233
    git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs for_testing
5.  affs: patches submitted, sit in Al Viro's tree:
    https://lkml.org/lkml/2012/6/6/400
    git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs for-next
6.  hfs: patches submitted, sit Andrew Morton's tree
    http://lkml.org/lkml/2012/6/12/82
7.  hfsplus: patches submitted, sit in Andrew Morton's tree:
    https://lkml.org/lkml/2012/6/13/195
8.  ext2:     done, see commit f72cf5e223a28d3b3ea7dc9e40464fd534e359e8
9.  vfat:     done, see commit 78491189ddb6d84d4a4abae992ed891a236d0263
10. jffs2:    done, see commit 208b14e507c00ff7f108e1a388dd3d8cc805a443
11. reiserfs: done, see commit 033369d1af1264abc23bea2e174aa47cdd212f6f

TODO: ufs

Thanks,
Artem.

[PATCHv7 1/5] ext4: Remove useless marking of superblock dirty

[Artem Bityutskiy]

From: Jan Kara <jack@suse.cz>

Commit a0375156 properly notes that superblock doesn't need to be marked
as dirty when only number of free inodes / blocks / number of directories
changes since that is recomputed on each mount anyway. However that comment
leaves some unnecessary markings as dirty in place. Remove these.

Artem: tested using xfstests for both journalled and non-journalled ext4.

Signed-off-by: Jan Kara <jack@suse.cz>
Tested-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
---
 fs/ext4/ialloc.c  |    2 --
 fs/ext4/mballoc.c |    2 --
 2 files changed, 0 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index d48e8b1..25b918c 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -315,7 +315,6 @@ out:
 		err = ext4_handle_dirty_metadata(handle, NULL, bitmap_bh);
 		if (!fatal)
 			fatal = err;
-		ext4_mark_super_dirty(sb);
 	} else
 		ext4_error(sb, "bit already cleared for inode %lu", ino);
 
@@ -830,7 +829,6 @@ got:
 	percpu_counter_dec(&sbi->s_freeinodes_counter);
 	if (S_ISDIR(mode))
 		percpu_counter_inc(&sbi->s_dirs_counter);
-	ext4_mark_super_dirty(sb);
 
 	if (sbi->s_log_groups_per_flex) {
 		flex_group = ext4_flex_group(sbi, group);
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 1cd6994..eabfb4c 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2825,7 +2825,6 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
 	err = ext4_handle_dirty_metadata(handle, NULL, gdp_bh);
 
 out_err:
-	ext4_mark_super_dirty(sb);
 	brelse(bitmap_bh);
 	return err;
 }
@@ -4694,7 +4693,6 @@ do_more:
 		put_bh(bitmap_bh);
 		goto do_more;
 	}
-	ext4_mark_super_dirty(sb);
 error_return:
 	brelse(bitmap_bh);
 	ext4_std_error(sb, err);
-- 
1.7.7.6

[PATCHv7 2/5] ext4: Convert last user of ext4_mark_super_dirty() to ext4_handle_dirty_super()

[Artem Bityutskiy]

From: Jan Kara <jack@suse.cz>

The last user of ext4_mark_super_dirty() in ext4_file_open() is so rare it
can well be modifying the superblock properly by journalling the change.
Change it and get rid of ext4_mark_super_dirty() as it's not needed anymore.

Artem: small amendments.
Artem: tested using xfstests for both journalled and non-journalled ext4.

Signed-off-by: Jan Kara <jack@suse.cz>
Tested-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
---
 fs/ext4/ext4.h |    9 ---------
 fs/ext4/file.c |   14 +++++++++++++-
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index cfc4e01..0c4042e 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2321,15 +2321,6 @@ static inline void ext4_unlock_group(struct super_block *sb,
 	spin_unlock(ext4_group_lock_ptr(sb, group));
 }
 
-static inline void ext4_mark_super_dirty(struct super_block *sb)
-{
-	struct ext4_super_block *es = EXT4_SB(sb)->s_es;
-
-	ext4_superblock_csum_set(sb, es);
-	if (EXT4_SB(sb)->s_journal == NULL)
-		sb->s_dirt =1;
-}
-
 /*
  * Block validity checking
  */
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 8c7642a..3a77494 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -181,9 +181,21 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
 		path.dentry = mnt->mnt_root;
 		cp = d_path(&path, buf, sizeof(buf));
 		if (!IS_ERR(cp)) {
+			handle_t *handle;
+			int err;
+
+			handle = ext4_journal_start_sb(sb, 1);
+			if (IS_ERR(handle))
+				return PTR_ERR(handle);
+			err = ext4_journal_get_write_access(handle, sbi->s_sbh);
+			if (err) {
+				ext4_journal_stop(handle);
+				return err;
+			}
 			strlcpy(sbi->s_es->s_last_mounted, cp,
 				sizeof(sbi->s_es->s_last_mounted));
-			ext4_mark_super_dirty(sb);
+			ext4_handle_dirty_super(handle, sb);
+			ext4_journal_stop(handle);
 		}
 	}
 	/*
-- 
1.7.7.6

[PATCHv7 3/5] ext4: remove unnecessary superblock dirtying

[Artem Bityutskiy]

From: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

This patch changes the 'ext4_handle_dirty_super()' function which submits
the superblock for I/O in the following cases:

1. When creating the first large file on a file system without
   EXT4_FEATURE_RO_COMPAT_LARGE_FILE feature.
2. When re-sizing the file-system.
3. When creating an xattr on a file-system without the
   EXT4_FEATURE_COMPAT_EXT_ATTR feature.

If the file-system has journal enabled, the superblock is written via the
journal. We do not modify this path.

If the file-system has no journal, this function, falls back to just marking
the superblock as dirty using the 's_dirt' superblock flag. This means that it
delays the actual superblock I/O submission by 5 seconds (default setting).
Namely, the 'sync_supers()' kernel thread will call 'ext4_write_super()' later
and will actually submit the superblock for I/O.

And this is the behavior this patch modifies: we stop using 's_dirt' and just
mark the superblock buffer as dirty right away. Indeed, all 3 cases above are
extremely rare and it does not add any value to delay the I/O submission for
them.

Note: 'ext4_handle_dirty_super()' executes '__ext4_handle_dirty_super()' with
'now = 0'. This patch basically makes the 'now' argument unneeded and it will
be deleted in one of the next patches.

This patch also removes 's_dirt' condition on the unmount path because we never
set it anymore, so we should not test it.

Tested using xfstests for both journalled and non-journalled ext4.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/ext4_jbd2.c |    5 ++---
 fs/ext4/super.c     |    2 +-
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/ext4_jbd2.c b/fs/ext4/ext4_jbd2.c
index 90f7c2e..c19ab6a 100644
--- a/fs/ext4/ext4_jbd2.c
+++ b/fs/ext4/ext4_jbd2.c
@@ -151,11 +151,10 @@ int __ext4_handle_dirty_super(const char *where, unsigned int line,
 		if (err)
 			ext4_journal_abort_handle(where, line, __func__,
 						  bh, handle, err);
-	} else if (now) {
+	} else {
 		ext4_superblock_csum_set(sb,
 				(struct ext4_super_block *)bh->b_data);
 		mark_buffer_dirty(bh);
-	} else
-		sb->s_dirt = 1;
+	}
 	return err;
 }
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index eb7aa3e..a391c53 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -896,7 +896,7 @@ static void ext4_put_super(struct super_block *sb)
 		EXT4_CLEAR_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER);
 		es->s_state = cpu_to_le16(sbi->s_mount_state);
 	}
-	if (sb->s_dirt || !(sb->s_flags & MS_RDONLY))
+	if (!(sb->s_flags & MS_RDONLY))
 		ext4_commit_super(sb, 1);
 
 	if (sbi->s_proc) {
-- 
1.7.7.6

[PATCHv7 4/5] ext4: weed out ext4_write_super

[Artem Bityutskiy]

From: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

We do not depend on VFS's '->write_super()' anymore and do not need the
's_dirt' flag anymore, so weed out 'ext4_write_super()' and 's_dirt'.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/super.c |   10 ----------
 1 files changed, 0 insertions(+), 10 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index a391c53..622d5c7 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -74,7 +74,6 @@ static const char *ext4_decode_error(struct super_block *sb, int errno,
 static int ext4_remount(struct super_block *sb, int *flags, char *data);
 static int ext4_statfs(struct dentry *dentry, struct kstatfs *buf);
 static int ext4_unfreeze(struct super_block *sb);
-static void ext4_write_super(struct super_block *sb);
 static int ext4_freeze(struct super_block *sb);
 static struct dentry *ext4_mount(struct file_system_type *fs_type, int flags,
 		       const char *dev_name, void *data);
@@ -1194,7 +1193,6 @@ static const struct super_operations ext4_nojournal_sops = {
 	.dirty_inode	= ext4_dirty_inode,
 	.drop_inode	= ext4_drop_inode,
 	.evict_inode	= ext4_evict_inode,
-	.write_super	= ext4_write_super,
 	.put_super	= ext4_put_super,
 	.statfs		= ext4_statfs,
 	.remount_fs	= ext4_remount,
@@ -4203,7 +4201,6 @@ static int ext4_commit_super(struct super_block *sb, int sync)
 	es->s_free_inodes_count =
 		cpu_to_le32(percpu_counter_sum_positive(
 				&EXT4_SB(sb)->s_freeinodes_counter));
-	sb->s_dirt = 0;
 	BUFFER_TRACE(sbh, "marking dirty");
 	ext4_superblock_csum_set(sb, es);
 	mark_buffer_dirty(sbh);
@@ -4310,13 +4307,6 @@ int ext4_force_commit(struct super_block *sb)
 	return ret;
 }
 
-static void ext4_write_super(struct super_block *sb)
-{
-	lock_super(sb);
-	ext4_commit_super(sb, 1);
-	unlock_super(sb);
-}
-
 static int ext4_sync_fs(struct super_block *sb, int wait)
 {
 	int ret = 0;
-- 
1.7.7.6

[PATCHv7 5/5] ext4: remove unnecessary argument

[Artem Bityutskiy]

From: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

The '__ext4_handle_dirty_metadata()' does not need the 'now' argument anymore
and we can kill it.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/ext4_jbd2.c |    3 +--
 fs/ext4/ext4_jbd2.h |    7 ++-----
 fs/ext4/inode.c     |    2 +-
 fs/ext4/namei.c     |    4 ++--
 fs/ext4/resize.c    |    2 +-
 5 files changed, 7 insertions(+), 11 deletions(-)

diff --git a/fs/ext4/ext4_jbd2.c b/fs/ext4/ext4_jbd2.c
index c19ab6a..bfa65b4 100644
--- a/fs/ext4/ext4_jbd2.c
+++ b/fs/ext4/ext4_jbd2.c
@@ -138,8 +138,7 @@ int __ext4_handle_dirty_metadata(const char *where, unsigned int line,
 }
 
 int __ext4_handle_dirty_super(const char *where, unsigned int line,
-			      handle_t *handle, struct super_block *sb,
-			      int now)
+			      handle_t *handle, struct super_block *sb)
 {
 	struct buffer_head *bh = EXT4_SB(sb)->s_sbh;
 	int err = 0;
diff --git a/fs/ext4/ext4_jbd2.h b/fs/ext4/ext4_jbd2.h
index f440e8f1..83b20fc 100644
--- a/fs/ext4/ext4_jbd2.h
+++ b/fs/ext4/ext4_jbd2.h
@@ -213,8 +213,7 @@ int __ext4_handle_dirty_metadata(const char *where, unsigned int line,
 				 struct buffer_head *bh);
 
 int __ext4_handle_dirty_super(const char *where, unsigned int line,
-			      handle_t *handle, struct super_block *sb,
-			      int now);
+			      handle_t *handle, struct super_block *sb);
 
 #define ext4_journal_get_write_access(handle, bh) \
 	__ext4_journal_get_write_access(__func__, __LINE__, (handle), (bh))
@@ -226,10 +225,8 @@ int __ext4_handle_dirty_super(const char *where, unsigned int line,
 #define ext4_handle_dirty_metadata(handle, inode, bh) \
 	__ext4_handle_dirty_metadata(__func__, __LINE__, (handle), (inode), \
 				     (bh))
-#define ext4_handle_dirty_super_now(handle, sb) \
-	__ext4_handle_dirty_super(__func__, __LINE__, (handle), (sb), 1)
 #define ext4_handle_dirty_super(handle, sb) \
-	__ext4_handle_dirty_super(__func__, __LINE__, (handle), (sb), 0)
+	__ext4_handle_dirty_super(__func__, __LINE__, (handle), (sb))
 
 handle_t *ext4_journal_start_sb(struct super_block *sb, int nblocks);
 int __ext4_journal_stop(const char *where, unsigned int line, handle_t *handle);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 02bc8cb..b1bd96f 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4034,7 +4034,7 @@ static int ext4_do_update_inode(handle_t *handle,
 			EXT4_SET_RO_COMPAT_FEATURE(sb,
 					EXT4_FEATURE_RO_COMPAT_LARGE_FILE);
 			ext4_handle_sync(handle);
-			err = ext4_handle_dirty_super_now(handle, sb);
+			err = ext4_handle_dirty_super(handle, sb);
 		}
 	}
 	raw_inode->i_generation = cpu_to_le32(inode->i_generation);
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 5845cd9..f155d57 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -2397,7 +2397,7 @@ int ext4_orphan_add(handle_t *handle, struct inode *inode)
 	/* Insert this inode at the head of the on-disk orphan list... */
 	NEXT_ORPHAN(inode) = le32_to_cpu(EXT4_SB(sb)->s_es->s_last_orphan);
 	EXT4_SB(sb)->s_es->s_last_orphan = cpu_to_le32(inode->i_ino);
-	err = ext4_handle_dirty_super_now(handle, sb);
+	err = ext4_handle_dirty_super(handle, sb);
 	rc = ext4_mark_iloc_dirty(handle, inode, &iloc);
 	if (!err)
 		err = rc;
@@ -2470,7 +2470,7 @@ int ext4_orphan_del(handle_t *handle, struct inode *inode)
 		if (err)
 			goto out_brelse;
 		sbi->s_es->s_last_orphan = cpu_to_le32(ino_next);
-		err = ext4_handle_dirty_super_now(handle, inode->i_sb);
+		err = ext4_handle_dirty_super(handle, inode->i_sb);
 	} else {
 		struct ext4_iloc iloc2;
 		struct inode *i_prev =
diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 7ea6cbb..09c7aae 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -798,7 +798,7 @@ static int add_new_gdb(handle_t *handle, struct inode *inode,
 	ext4_kvfree(o_group_desc);
 
 	le16_add_cpu(&es->s_reserved_gdt_blocks, -1);
-	err = ext4_handle_dirty_super_now(handle, sb);
+	err = ext4_handle_dirty_super(handle, sb);
 	if (err)
 		ext4_std_error(sb, err);
 
-- 
1.7.7.6

Re: [PATCHv7 0/5] ext4: stop using write_supers and s_dirt

[Artem Bityutskiy]

[-- Attachment #1: Type: text/plain, Size: 819 bytes --]

On Wed, 2012-07-11 at 16:46 +0300, Artem Bityutskiy wrote:
> This patch-set makes ext4 file-system stop using the VFS '->write_supers()'
> call-back and the '->s_dirt' superblock field because I plan to remove them
> once all users are gone.

Hi Ted, is there any chance for this stuff to hit 3.6?

Basically I have 3 pending file-systems:
1. ext4 (these patches)
2. sysv - trivial, I hope Andrew would pick them.
3. ufs - should be straight-forward to change the same way I changed
hfs. I'll send patches soon. I hope Andrew would pick them as well.

Everything else - either in upstream or in -mm or in sub-system trees.

After this, I can kill sync_supers and have a chance that Linus would
accept the patches at 3.6-rc1, and end up with sync_super-less 3.6.

-- 
Best Regards,
Artem Bityutskiy

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 836 bytes --]

Re: [PATCHv7 0/5] ext4: stop using write_supers and s_dirt

[Theodore Ts'o]

On Wed, Jul 11, 2012 at 04:46:39PM +0300, Artem Bityutskiy wrote:
> This patch-set makes ext4 file-system stop using the VFS '->write_supers()'
> call-back and the '->s_dirt' superblock field because I plan to remove them
> once all users are gone.

I've applied this patch series, thanks.

							- Ted