+ task_struct-make-journal_info-conditional.patch added to -mm tree

+ task_struct-make-journal_info-conditional.patch added to -mm tree

[akpm]

The patch titled
     task_struct: make journal_info conditional
has been added to the -mm tree.  Its filename is
     task_struct-make-journal_info-conditional.patch

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/SubmitChecklist when testing your code ***

See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this

The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/

------------------------------------------------------
Subject: task_struct: make journal_info conditional
From: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>

journal_info in task_struct is used in journaling file system only.  So
introduce CONFIG_FS_JOURNAL_INFO and make it conditional.

Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: KONISHI Ryusuke <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/Kconfig                |    4 ++++
 fs/btrfs/Kconfig          |    1 +
 fs/ext4/Kconfig           |    1 +
 fs/gfs2/Kconfig           |    1 +
 fs/jbd/Kconfig            |    1 +
 fs/jbd2/Kconfig           |    1 +
 fs/nilfs2/Kconfig         |    1 +
 fs/reiserfs/Kconfig       |    1 +
 include/linux/init_task.h |    8 +++++++-
 include/linux/sched.h     |    2 ++
 10 files changed, 20 insertions(+), 1 deletion(-)

diff -puN fs/Kconfig~task_struct-make-journal_info-conditional fs/Kconfig
--- a/fs/Kconfig~task_struct-make-journal_info-conditional
+++ a/fs/Kconfig
@@ -6,6 +6,10 @@ menu "File systems"
 
 if BLOCK
 
+config FS_JOURNAL_INFO
+	bool
+	default n
+
 source "fs/ext2/Kconfig"
 source "fs/ext3/Kconfig"
 source "fs/ext4/Kconfig"
diff -puN fs/btrfs/Kconfig~task_struct-make-journal_info-conditional fs/btrfs/Kconfig
--- a/fs/btrfs/Kconfig~task_struct-make-journal_info-conditional
+++ a/fs/btrfs/Kconfig
@@ -4,6 +4,7 @@ config BTRFS_FS
 	select LIBCRC32C
 	select ZLIB_INFLATE
 	select ZLIB_DEFLATE
+	select FS_JOURNAL_INFO
 	help
 	  Btrfs is a new filesystem with extents, writable snapshotting,
 	  support for multiple devices and many more features.
diff -puN fs/ext4/Kconfig~task_struct-make-journal_info-conditional fs/ext4/Kconfig
--- a/fs/ext4/Kconfig~task_struct-make-journal_info-conditional
+++ a/fs/ext4/Kconfig
@@ -2,6 +2,7 @@ config EXT4_FS
 	tristate "The Extended 4 (ext4) filesystem"
 	select JBD2
 	select CRC16
+	select FS_JOURNAL_INFO
 	help
 	  This is the next generation of the ext3 filesystem.
 
diff -puN fs/gfs2/Kconfig~task_struct-make-journal_info-conditional fs/gfs2/Kconfig
--- a/fs/gfs2/Kconfig~task_struct-make-journal_info-conditional
+++ a/fs/gfs2/Kconfig
@@ -10,6 +10,7 @@ config GFS2_FS
 	select SLOW_WORK
 	select QUOTA
 	select QUOTACTL
+	select FS_JOURNAL_INFO
 	help
 	  A cluster filesystem.
 
diff -puN fs/jbd/Kconfig~task_struct-make-journal_info-conditional fs/jbd/Kconfig
--- a/fs/jbd/Kconfig~task_struct-make-journal_info-conditional
+++ a/fs/jbd/Kconfig
@@ -1,5 +1,6 @@
 config JBD
 	tristate
+	select FS_JOURNAL_INFO
 	help
 	  This is a generic journalling layer for block devices.  It is
 	  currently used by the ext3 file system, but it could also be
diff -puN fs/jbd2/Kconfig~task_struct-make-journal_info-conditional fs/jbd2/Kconfig
--- a/fs/jbd2/Kconfig~task_struct-make-journal_info-conditional
+++ a/fs/jbd2/Kconfig
@@ -1,6 +1,7 @@
 config JBD2
 	tristate
 	select CRC32
+	select FS_JOURNAL_INFO
 	help
 	  This is a generic journaling layer for block devices that support
 	  both 32-bit and 64-bit block numbers.  It is currently used by
diff -puN fs/nilfs2/Kconfig~task_struct-make-journal_info-conditional fs/nilfs2/Kconfig
--- a/fs/nilfs2/Kconfig~task_struct-make-journal_info-conditional
+++ a/fs/nilfs2/Kconfig
@@ -2,6 +2,7 @@ config NILFS2_FS
 	tristate "NILFS2 file system support (EXPERIMENTAL)"
 	depends on EXPERIMENTAL
 	select CRC32
+	select FS_JOURNAL_INFO
 	help
 	  NILFS2 is a log-structured file system (LFS) supporting continuous
 	  snapshotting.  In addition to versioning capability of the entire
diff -puN fs/reiserfs/Kconfig~task_struct-make-journal_info-conditional fs/reiserfs/Kconfig
--- a/fs/reiserfs/Kconfig~task_struct-make-journal_info-conditional
+++ a/fs/reiserfs/Kconfig
@@ -1,6 +1,7 @@
 config REISERFS_FS
 	tristate "Reiserfs support"
 	select CRC32
+	select FS_JOURNAL_INFO
 	help
 	  Stores not just filenames but the files themselves in a balanced
 	  tree.  Uses journalling.
diff -puN include/linux/init_task.h~task_struct-make-journal_info-conditional include/linux/init_task.h
--- a/include/linux/init_task.h~task_struct-make-journal_info-conditional
+++ a/include/linux/init_task.h
@@ -111,6 +111,12 @@ extern struct cred init_cred;
 # define INIT_PERF_EVENTS(tsk)
 #endif
 
+#ifdef CONFIG_FS_JOURNAL_INFO
+#define INIT_JOURNAL_INFO	.journal_info = NULL,
+#else
+#define INIT_JOURNAL_INFO
+#endif
+
 /*
  *  INIT_TASK is used to set up the first task table, touch at
  * your own risk!. Base=0, limit=0x1fffff (=2MB)
@@ -162,7 +168,6 @@ extern struct cred init_cred;
 		.signal = {{0}}},					\
 	.blocked	= {{0}},					\
 	.alloc_lock	= __SPIN_LOCK_UNLOCKED(tsk.alloc_lock),		\
-	.journal_info	= NULL,						\
 	.cpu_timers	= INIT_CPU_TIMERS(tsk.cpu_timers),		\
 	.fs_excl	= ATOMIC_INIT(0),				\
 	.pi_lock	= __SPIN_LOCK_UNLOCKED(tsk.pi_lock),		\
@@ -173,6 +178,7 @@ extern struct cred init_cred;
 		[PIDTYPE_SID]  = INIT_PID_LINK(PIDTYPE_SID),		\
 	},								\
 	.dirties = INIT_PROP_LOCAL_SINGLE(dirties),			\
+	INIT_JOURNAL_INFO						\
 	INIT_IDS							\
 	INIT_PERF_EVENTS(tsk)						\
 	INIT_TRACE_IRQFLAGS						\
diff -puN include/linux/sched.h~task_struct-make-journal_info-conditional include/linux/sched.h
--- a/include/linux/sched.h~task_struct-make-journal_info-conditional
+++ a/include/linux/sched.h
@@ -1452,8 +1452,10 @@ struct task_struct {
 	gfp_t lockdep_reclaim_gfp;
 #endif
 
+#ifdef CONFIG_FS_JOURNAL_INFO
 /* journalling filesystem info */
 	void *journal_info;
+#endif
 
 /* stacked block device info */
 	struct bio *bio_list, **bio_tail;
_

Patches currently in -mm which might be from h-shimamoto@ct.jp.nec.com are

linux-next.patch
kernelh-add-printk_ratelimited-and-pr_level_rl.patch
kernelh-add-printk_ratelimited-and-pr_level_rl-checkpatch-fixes.patch
kernelh-add-printk_ratelimited-and-pr_level_rl-rename.patch
task_struct-make-journal_info-conditional.patch

Re: + task_struct-make-journal_info-conditional.patch added to -mm tree

[Alexey Dobriyan]

On Thu, Dec 03, 2009 at 02:40:57PM -0800, akpm@linux-foundation.org wrote:
> --- a/include/linux/sched.h~task_struct-make-journal_info-conditional
> +++ a/include/linux/sched.h
> @@ -1452,8 +1452,10 @@ struct task_struct {
>  	gfp_t lockdep_reclaim_gfp;
>  #endif
>  
> +#ifdef CONFIG_FS_JOURNAL_INFO
>  /* journalling filesystem info */
>  	void *journal_info;
> +#endif

This will prevent using e.g. ext3 on CONFIG_EXT3_FS=n kernels.

Re: + task_struct-make-journal_info-conditional.patch added to -mm tree

[Hiroshi Shimamoto]

Alexey Dobriyan wrote:
> On Thu, Dec 03, 2009 at 02:40:57PM -0800, akpm@linux-foundation.org wrote:
>> --- a/include/linux/sched.h~task_struct-make-journal_info-conditional
>> +++ a/include/linux/sched.h
>> @@ -1452,8 +1452,10 @@ struct task_struct {
>>  	gfp_t lockdep_reclaim_gfp;
>>  #endif
>>  
>> +#ifdef CONFIG_FS_JOURNAL_INFO
>>  /* journalling filesystem info */
>>  	void *journal_info;
>> +#endif
> 
> This will prevent using e.g. ext3 on CONFIG_EXT3_FS=n kernels.

I'm sorry, I'm not sure what you're mentioning.

Thanks,
Hiroshi

Re: + task_struct-make-journal_info-conditional.patch added to -mm tree

[Alexey Dobriyan]

On Fri, Dec 04, 2009 at 12:58:06PM +0900, Hiroshi Shimamoto wrote:
> Alexey Dobriyan wrote:
> > On Thu, Dec 03, 2009 at 02:40:57PM -0800, akpm@linux-foundation.org wrote:
> >> --- a/include/linux/sched.h~task_struct-make-journal_info-conditional
> >> +++ a/include/linux/sched.h
> >> @@ -1452,8 +1452,10 @@ struct task_struct {
> >>  	gfp_t lockdep_reclaim_gfp;
> >>  #endif
> >>  
> >> +#ifdef CONFIG_FS_JOURNAL_INFO
> >>  /* journalling filesystem info */
> >>  	void *journal_info;
> >> +#endif
> > 
> > This will prevent using e.g. ext3 on CONFIG_EXT3_FS=n kernels.
> 
> I'm sorry, I'm not sure what you're mentioning.

With this patch admin must decide in advance if he will ever use ext3.
EXT3_FS=n kernels won't be able to get ext3 support without reboot
even as module, because task_struct will be different.

Which is a regression compared to current state.

The biggest example of such behaviour is ipv6 module, but it should not
be spread more.

Re: + task_struct-make-journal_info-conditional.patch added to -mm tree

[Steven Whitehouse]

Hi,

On Fri, 2009-12-04 at 08:17 +0300, Alexey Dobriyan wrote:
> On Fri, Dec 04, 2009 at 12:58:06PM +0900, Hiroshi Shimamoto wrote:
> > Alexey Dobriyan wrote:
> > > On Thu, Dec 03, 2009 at 02:40:57PM -0800, akpm@linux-foundation.org wrote:
> > >> --- a/include/linux/sched.h~task_struct-make-journal_info-conditional
> > >> +++ a/include/linux/sched.h
> > >> @@ -1452,8 +1452,10 @@ struct task_struct {
> > >>  	gfp_t lockdep_reclaim_gfp;
> > >>  #endif
> > >>  
> > >> +#ifdef CONFIG_FS_JOURNAL_INFO
> > >>  /* journalling filesystem info */
> > >>  	void *journal_info;
> > >> +#endif
> > > 
> > > This will prevent using e.g. ext3 on CONFIG_EXT3_FS=n kernels.
> > 
> > I'm sorry, I'm not sure what you're mentioning.
> 
> With this patch admin must decide in advance if he will ever use ext3.
> EXT3_FS=n kernels won't be able to get ext3 support without reboot
> even as module, because task_struct will be different.
> 
> Which is a regression compared to current state.
> 
> The biggest example of such behaviour is ipv6 module, but it should not
> be spread more.

I agree. If we want to be rid of this then I think we should simply pass
the journal info as a parameter through the relevant filesystems (is
there any reason why we do things this way? I couldn't think of one) and
thus avoid the use of this field in the first place,

Steve.

Re: + task_struct-make-journal_info-conditional.patch added to -mm tree

[Hiroshi Shimamoto]

Alexey Dobriyan wrote:
> On Fri, Dec 04, 2009 at 12:58:06PM +0900, Hiroshi Shimamoto wrote:
>> Alexey Dobriyan wrote:
>>> On Thu, Dec 03, 2009 at 02:40:57PM -0800, akpm@linux-foundation.org wrote:
>>>> --- a/include/linux/sched.h~task_struct-make-journal_info-conditional
>>>> +++ a/include/linux/sched.h
>>>> @@ -1452,8 +1452,10 @@ struct task_struct {
>>>>  	gfp_t lockdep_reclaim_gfp;
>>>>  #endif
>>>>  
>>>> +#ifdef CONFIG_FS_JOURNAL_INFO
>>>>  /* journalling filesystem info */
>>>>  	void *journal_info;
>>>> +#endif
>>> This will prevent using e.g. ext3 on CONFIG_EXT3_FS=n kernels.
>> I'm sorry, I'm not sure what you're mentioning.
> 
> With this patch admin must decide in advance if he will ever use ext3.
> EXT3_FS=n kernels won't be able to get ext3 support without reboot
> even as module, because task_struct will be different.

I see, you want to keep this field for future use even if EXT3_FS=n.
I think, however, there might be a need to remove this because the user
never enable any journaling filesystem.

> 
> Which is a regression compared to current state.

I understand it's a regression, so how about make this option Y by
default?

====
From: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Subject: [PATCH v2] task_struct: make journal_info conditional

journal_info in task_struct is used in journaling file system only.
So introduce CONFIG_FS_JOURNAL_INFO and make it conditional.

Signed-off-by: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
CC: Chris Mason <chris.mason@oracle.com>
CC: "Theodore Ts'o" <tytso@mit.edu>
CC: Steven Whitehouse <swhiteho@redhat.com>
CC: KONISHI Ryusuke <konishi.ryusuke@lab.ntt.co.jp>
CC: Andrew Morton <akpm@linux-foundation.org>
---
v1->v2: Make FS_JOURNAL_INFO Y by default, and add help document.

 fs/Kconfig                |   12 ++++++++++++
 fs/btrfs/Kconfig          |    1 +
 fs/ext4/Kconfig           |    1 +
 fs/gfs2/Kconfig           |    1 +
 fs/jbd/Kconfig            |    1 +
 fs/jbd2/Kconfig           |    1 +
 fs/nilfs2/Kconfig         |    1 +
 fs/reiserfs/Kconfig       |    1 +
 include/linux/init_task.h |    8 +++++++-
 include/linux/sched.h     |    2 ++
 10 files changed, 28 insertions(+), 1 deletions(-)

diff --git a/fs/Kconfig b/fs/Kconfig
index 2aa5663..a684c1b 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -6,6 +6,18 @@ menu "File systems"
 
 if BLOCK
 
+config FS_JOURNAL_INFO
+	bool "Include FS Journal Info in task struct"
+	default y
+	help
+	  Include Journal Information in task struct for journaling filesystem.
+	  It used in Btrfs, EXT3, EXT4, GFS2, NILFS2 and Reiserfs.
+	  If you say N, remove the field for journal info from task struct, it
+	  reduces task struct size but disables to support the above journaling
+	  filesystems.
+
+	  Say Y if unsure.
+
 source "fs/ext2/Kconfig"
 source "fs/ext3/Kconfig"
 source "fs/ext4/Kconfig"
diff --git a/fs/btrfs/Kconfig b/fs/btrfs/Kconfig
index 7bb3c02..402afe0 100644
--- a/fs/btrfs/Kconfig
+++ b/fs/btrfs/Kconfig
@@ -4,6 +4,7 @@ config BTRFS_FS
 	select LIBCRC32C
 	select ZLIB_INFLATE
 	select ZLIB_DEFLATE
+	select FS_JOURNAL_INFO
 	help
 	  Btrfs is a new filesystem with extents, writable snapshotting,
 	  support for multiple devices and many more features.
diff --git a/fs/ext4/Kconfig b/fs/ext4/Kconfig
index 9f2d45d..464b486 100644
--- a/fs/ext4/Kconfig
+++ b/fs/ext4/Kconfig
@@ -2,6 +2,7 @@ config EXT4_FS
 	tristate "The Extended 4 (ext4) filesystem"
 	select JBD2
 	select CRC16
+	select FS_JOURNAL_INFO
 	help
 	  This is the next generation of the ext3 filesystem.
 
diff --git a/fs/gfs2/Kconfig b/fs/gfs2/Kconfig
index 4dcddf8..b192c66 100644
--- a/fs/gfs2/Kconfig
+++ b/fs/gfs2/Kconfig
@@ -10,6 +10,7 @@ config GFS2_FS
 	select SLOW_WORK
 	select QUOTA
 	select QUOTACTL
+	select FS_JOURNAL_INFO
 	help
 	  A cluster filesystem.
 
diff --git a/fs/jbd/Kconfig b/fs/jbd/Kconfig
index 4e28bee..a840898 100644
--- a/fs/jbd/Kconfig
+++ b/fs/jbd/Kconfig
@@ -1,5 +1,6 @@
 config JBD
 	tristate
+	select FS_JOURNAL_INFO
 	help
 	  This is a generic journalling layer for block devices.  It is
 	  currently used by the ext3 file system, but it could also be
diff --git a/fs/jbd2/Kconfig b/fs/jbd2/Kconfig
index f32f346..0f7d1ce 100644
--- a/fs/jbd2/Kconfig
+++ b/fs/jbd2/Kconfig
@@ -1,6 +1,7 @@
 config JBD2
 	tristate
 	select CRC32
+	select FS_JOURNAL_INFO
 	help
 	  This is a generic journaling layer for block devices that support
 	  both 32-bit and 64-bit block numbers.  It is currently used by
diff --git a/fs/nilfs2/Kconfig b/fs/nilfs2/Kconfig
index 251da07..1225af7 100644
--- a/fs/nilfs2/Kconfig
+++ b/fs/nilfs2/Kconfig
@@ -2,6 +2,7 @@ config NILFS2_FS
 	tristate "NILFS2 file system support (EXPERIMENTAL)"
 	depends on EXPERIMENTAL
 	select CRC32
+	select FS_JOURNAL_INFO
 	help
 	  NILFS2 is a log-structured file system (LFS) supporting continuous
 	  snapshotting.  In addition to versioning capability of the entire
diff --git a/fs/reiserfs/Kconfig b/fs/reiserfs/Kconfig
index 513f431..ac7cd75 100644
--- a/fs/reiserfs/Kconfig
+++ b/fs/reiserfs/Kconfig
@@ -1,6 +1,7 @@
 config REISERFS_FS
 	tristate "Reiserfs support"
 	select CRC32
+	select FS_JOURNAL_INFO
 	help
 	  Stores not just filenames but the files themselves in a balanced
 	  tree.  Uses journalling.
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 8d10aa7..8ed0abf 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -111,6 +111,12 @@ extern struct cred init_cred;
 # define INIT_PERF_EVENTS(tsk)
 #endif
 
+#ifdef CONFIG_FS_JOURNAL_INFO
+#define INIT_JOURNAL_INFO	.journal_info = NULL,
+#else
+#define INIT_JOURNAL_INFO
+#endif
+
 /*
  *  INIT_TASK is used to set up the first task table, touch at
  * your own risk!. Base=0, limit=0x1fffff (=2MB)
@@ -162,7 +168,6 @@ extern struct cred init_cred;
 		.signal = {{0}}},					\
 	.blocked	= {{0}},					\
 	.alloc_lock	= __SPIN_LOCK_UNLOCKED(tsk.alloc_lock),		\
-	.journal_info	= NULL,						\
 	.cpu_timers	= INIT_CPU_TIMERS(tsk.cpu_timers),		\
 	.fs_excl	= ATOMIC_INIT(0),				\
 	.pi_lock	= __SPIN_LOCK_UNLOCKED(tsk.pi_lock),		\
@@ -173,6 +178,7 @@ extern struct cred init_cred;
 		[PIDTYPE_SID]  = INIT_PID_LINK(PIDTYPE_SID),		\
 	},								\
 	.dirties = INIT_PROP_LOCAL_SINGLE(dirties),			\
+	INIT_JOURNAL_INFO						\
 	INIT_IDS							\
 	INIT_PERF_EVENTS(tsk)						\
 	INIT_TRACE_IRQFLAGS						\
diff --git a/include/linux/sched.h b/include/linux/sched.h
index c13c43e..92b1325 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1452,8 +1452,10 @@ struct task_struct {
 	gfp_t lockdep_reclaim_gfp;
 #endif
 
+#ifdef CONFIG_FS_JOURNAL_INFO
 /* journalling filesystem info */
 	void *journal_info;
+#endif
 
 /* stacked block device info */
 	struct bio *bio_list, **bio_tail;
-- 
1.6.5.5

Re: + task_struct-make-journal_info-conditional.patch added to -mm tree

[Alexey Dobriyan]

On 12/7/09, Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com> wrote:
> I understand it's a regression, so how about make this option Y by
> default?

Sorry, this is still loss in functionality for just one pointer in task_struct.

Re: + task_struct-make-journal_info-conditional.patch added to -mm tree

[Ryusuke Konishi]

>Alexey Dobriyan wrote:
>> On Fri, Dec 04, 2009 at 12:58:06PM +0900, Hiroshi Shimamoto wrote:
>>> Alexey Dobriyan wrote:
>>>> On Thu, Dec 03, 2009 at 02:40:57PM -0800, akpm@linux-foundation.org wrote:
>>>>> --- a/include/linux/sched.h~task_struct-make-journal_info-conditional
>>>>> +++ a/include/linux/sched.h
>>>>> @@ -1452,8 +1452,10 @@ struct task_struct {
>>>>>  	gfp_t lockdep_reclaim_gfp;
>>>>>  #endif
>>>>>  
>>>>> +#ifdef CONFIG_FS_JOURNAL_INFO
>>>>>  /* journalling filesystem info */
>>>>>  	void *journal_info;
>>>>> +#endif
>>>> This will prevent using e.g. ext3 on CONFIG_EXT3_FS=n kernels.
>>> I'm sorry, I'm not sure what you're mentioning.
>> 
>> With this patch admin must decide in advance if he will ever use ext3.
>> EXT3_FS=n kernels won't be able to get ext3 support without reboot
>> even as module, because task_struct will be different.
>
>I see, you want to keep this field for future use even if EXT3_FS=n.
>I think, however, there might be a need to remove this because the user
>never enable any journaling filesystem.

Do you have some background to remove the "void *" from task_struct?
You need it for embedded purpose?

Ryusuke Konishi

Re: + task_struct-make-journal_info-conditional.patch added to -mm tree

[Hiroshi Shimamoto]

Ryusuke Konishi wrote:
>> Alexey Dobriyan wrote:
>>> On Fri, Dec 04, 2009 at 12:58:06PM +0900, Hiroshi Shimamoto wrote:
>>>> Alexey Dobriyan wrote:
>>>>> On Thu, Dec 03, 2009 at 02:40:57PM -0800, akpm@linux-foundation.org wrote:
>>>>>> --- a/include/linux/sched.h~task_struct-make-journal_info-conditional
>>>>>> +++ a/include/linux/sched.h
>>>>>> @@ -1452,8 +1452,10 @@ struct task_struct {
>>>>>>  	gfp_t lockdep_reclaim_gfp;
>>>>>>  #endif
>>>>>>  
>>>>>> +#ifdef CONFIG_FS_JOURNAL_INFO
>>>>>>  /* journalling filesystem info */
>>>>>>  	void *journal_info;
>>>>>> +#endif
>>>>> This will prevent using e.g. ext3 on CONFIG_EXT3_FS=n kernels.
>>>> I'm sorry, I'm not sure what you're mentioning.
>>> With this patch admin must decide in advance if he will ever use ext3.
>>> EXT3_FS=n kernels won't be able to get ext3 support without reboot
>>> even as module, because task_struct will be different.
>> I see, you want to keep this field for future use even if EXT3_FS=n.
>> I think, however, there might be a need to remove this because the user
>> never enable any journaling filesystem.
> 
> Do you have some background to remove the "void *" from task_struct?
> You need it for embedded purpose?

Yeah, it's for embedded. I think it's good if there is a option to make
memory usage small.

Thanks,
Hiroshi