From: Saugata Das <[email protected]>
Today, storage devices like eMMC has special features like data tagging
(introduced in MMC-4.5 version) in order to improve performance of some
specific writes. On MMC stack, data tagging is used for all writes which
has REQ_META flag set. This patch adds the capability to add REQ_META flag
during meta data write.
Signed-off-by: Saugata Das <[email protected]>
---
fs/buffer.c | 10 ++++++++--
include/linux/buffer_head.h | 2 ++
2 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/fs/buffer.c b/fs/buffer.c
index 36d6665..688b38b 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1685,7 +1685,10 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
do {
struct buffer_head *next = bh->b_this_page;
if (buffer_async_write(bh)) {
- submit_bh(write_op, bh);
+ if (buffer_meta(bh))
+ submit_bh(write_op | REQ_META, bh);
+ else
+ submit_bh(write_op, bh);
nr_underway++;
}
bh = next;
@@ -1739,7 +1742,10 @@ recover:
struct buffer_head *next = bh->b_this_page;
if (buffer_async_write(bh)) {
clear_buffer_dirty(bh);
- submit_bh(write_op, bh);
+ if (buffer_meta(bh))
+ submit_bh(write_op | REQ_META, bh);
+ else
+ submit_bh(write_op, bh);
nr_underway++;
}
bh = next;
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index ef26043..0776564 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -34,6 +34,7 @@ enum bh_state_bits {
BH_Write_EIO, /* I/O error on write */
BH_Unwritten, /* Buffer is allocated on disk but not written */
BH_Quiet, /* Buffer Error Prinks to be quiet */
+ BH_Meta, /* Is meta */
BH_PrivateStart,/* not a state bit, but the first bit available
* for private allocation by other entities
@@ -126,6 +127,7 @@ BUFFER_FNS(Delay, delay)
BUFFER_FNS(Boundary, boundary)
BUFFER_FNS(Write_EIO, write_io_error)
BUFFER_FNS(Unwritten, unwritten)
+BUFFER_FNS(Meta, meta)
#define bh_offset(bh) ((unsigned long)(bh)->b_data & ~PAGE_MASK)
#define touch_buffer(bh) mark_page_accessed(bh->b_page)
--
1.7.4.3
From: Saugata Das <[email protected]>
Today, storage devices like eMMC has special features like data tagging
(introduced in MMC-4.5 version) in order to improve performance of some
specific writes. On MMC stack, data tagging is used for all writes which has
REQ_META flag set. On EXT4, however, currently REQ_META is set only for read.
This patch adds the capability mark a meta-data buffer with set_buffer_meta
during meta data write. During submit_bh, this information is used to set
REQ_META flag.
Signed-off-by: Saugata Das <[email protected]>
---
fs/ext4/ext4_jbd2.c | 4 ++++
fs/ext4/inode.c | 4 +++-
2 files changed, 7 insertions(+), 1 deletions(-)
diff --git a/fs/ext4/ext4_jbd2.c b/fs/ext4/ext4_jbd2.c
index aca1790..097c062 100644
--- a/fs/ext4/ext4_jbd2.c
+++ b/fs/ext4/ext4_jbd2.c
@@ -107,6 +107,8 @@ int __ext4_handle_dirty_metadata(const char *where, unsigned int line,
{
int err = 0;
+ set_buffer_meta(bh);
+
if (ext4_handle_valid(handle)) {
err = jbd2_journal_dirty_metadata(handle, bh);
if (err) {
@@ -143,6 +145,8 @@ int __ext4_handle_dirty_super(const char *where, unsigned int line,
struct buffer_head *bh = EXT4_SB(sb)->s_sbh;
int err = 0;
+ set_buffer_meta(bh);
+
if (ext4_handle_valid(handle)) {
err = jbd2_journal_dirty_metadata(handle, bh);
if (err)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c77b0bd..754fe77 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4035,8 +4035,10 @@ int ext4_write_inode(struct inode *inode, struct writeback_control *wbc)
err = __ext4_get_inode_loc(inode, &iloc, 0);
if (err)
return err;
- if (wbc->sync_mode == WB_SYNC_ALL)
+ if (wbc->sync_mode == WB_SYNC_ALL) {
+ set_buffer_meta(iloc.bh);
sync_dirty_buffer(iloc.bh);
+ }
if (buffer_req(iloc.bh) && !buffer_uptodate(iloc.bh)) {
EXT4_ERROR_INODE_BLOCK(inode, iloc.bh->b_blocknr,
"IO error syncing inode");
--
1.7.4.3
Hi,
On Fri, 11 May 2012 20:32:56 +0530, Saugata Das wrote:
> From: Saugata Das <[email protected]>
>
> Today, storage devices like eMMC has special features like data tagging
> (introduced in MMC-4.5 version) in order to improve performance of some
> specific writes. On MMC stack, data tagging is used for all writes which
> has REQ_META flag set. This patch adds the capability to add REQ_META flag
> during meta data write.
>
AFAIK, the REQ_META is only for marking a bio/req to be recognized when
using blktrace or something. You can use REQ_PRIO for the purpose but it
applies only if your ioscheduler is CFQ.
But I'm not aware how the MMC stack works, so I might be missing something.
Thanks,
Namhyung
> Signed-off-by: Saugata Das <[email protected]>
> ---
> fs/buffer.c | 10 ++++++++--
> include/linux/buffer_head.h | 2 ++
> 2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 36d6665..688b38b 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1685,7 +1685,10 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
> do {
> struct buffer_head *next = bh->b_this_page;
> if (buffer_async_write(bh)) {
> - submit_bh(write_op, bh);
> + if (buffer_meta(bh))
> + submit_bh(write_op | REQ_META, bh);
> + else
> + submit_bh(write_op, bh);
> nr_underway++;
> }
> bh = next;
> @@ -1739,7 +1742,10 @@ recover:
> struct buffer_head *next = bh->b_this_page;
> if (buffer_async_write(bh)) {
> clear_buffer_dirty(bh);
> - submit_bh(write_op, bh);
> + if (buffer_meta(bh))
> + submit_bh(write_op | REQ_META, bh);
> + else
> + submit_bh(write_op, bh);
> nr_underway++;
> }
> bh = next;
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> index ef26043..0776564 100644
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -34,6 +34,7 @@ enum bh_state_bits {
> BH_Write_EIO, /* I/O error on write */
> BH_Unwritten, /* Buffer is allocated on disk but not written */
> BH_Quiet, /* Buffer Error Prinks to be quiet */
> + BH_Meta, /* Is meta */
>
> BH_PrivateStart,/* not a state bit, but the first bit available
> * for private allocation by other entities
> @@ -126,6 +127,7 @@ BUFFER_FNS(Delay, delay)
> BUFFER_FNS(Boundary, boundary)
> BUFFER_FNS(Write_EIO, write_io_error)
> BUFFER_FNS(Unwritten, unwritten)
> +BUFFER_FNS(Meta, meta)
>
> #define bh_offset(bh) ((unsigned long)(bh)->b_data & ~PAGE_MASK)
> #define touch_buffer(bh) mark_page_accessed(bh->b_page)
On 14 May 2012 07:12, Namhyung Kim <[email protected]> wrote:
> Hi,
>
> On Fri, 11 May 2012 20:32:56 +0530, Saugata Das wrote:
>> From: Saugata Das <[email protected]>
>>
>> Today, storage devices like eMMC has special features like data tagging
>> (introduced in MMC-4.5 version) in order to improve performance of some
>> specific writes. On MMC stack, data tagging is used for all writes which
>> has REQ_META flag set. This patch adds the capability to add REQ_META flag
>> during meta data write.
>>
>
> AFAIK, the REQ_META is only for marking a bio/req to be recognized when
> using blktrace or something. You can use REQ_PRIO for the purpose but it
> applies only if your ioscheduler is CFQ.
>
> But I'm not aware how the MMC stack works, so I might be missing something.
>
Today on ext4, REQ_META or REQ_PRIO are only used during read
operation. For meta-data writes, no special flag (REQ_META or
REQ_PRIO) is set.
On eMMC, we depend on REQ_META flag to implement the "reliable write"
and "data tag" feature, which are linked with additional reliability
and performance for file system meta-data writes.
> Thanks,
> Namhyung
>
>
>> Signed-off-by: Saugata Das <[email protected]>
>> ---
>> ?fs/buffer.c ? ? ? ? ? ? ? ? | ? 10 ++++++++--
>> ?include/linux/buffer_head.h | ? ?2 ++
>> ?2 files changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/buffer.c b/fs/buffer.c
>> index 36d6665..688b38b 100644
>> --- a/fs/buffer.c
>> +++ b/fs/buffer.c
>> @@ -1685,7 +1685,10 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
>> ? ? ? do {
>> ? ? ? ? ? ? ? struct buffer_head *next = bh->b_this_page;
>> ? ? ? ? ? ? ? if (buffer_async_write(bh)) {
>> - ? ? ? ? ? ? ? ? ? ? submit_bh(write_op, bh);
>> + ? ? ? ? ? ? ? ? ? ? if (buffer_meta(bh))
>> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? submit_bh(write_op | REQ_META, bh);
>> + ? ? ? ? ? ? ? ? ? ? else
>> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? submit_bh(write_op, bh);
>> ? ? ? ? ? ? ? ? ? ? ? nr_underway++;
>> ? ? ? ? ? ? ? }
>> ? ? ? ? ? ? ? bh = next;
>> @@ -1739,7 +1742,10 @@ recover:
>> ? ? ? ? ? ? ? struct buffer_head *next = bh->b_this_page;
>> ? ? ? ? ? ? ? if (buffer_async_write(bh)) {
>> ? ? ? ? ? ? ? ? ? ? ? clear_buffer_dirty(bh);
>> - ? ? ? ? ? ? ? ? ? ? submit_bh(write_op, bh);
>> + ? ? ? ? ? ? ? ? ? ? if (buffer_meta(bh))
>> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? submit_bh(write_op | REQ_META, bh);
>> + ? ? ? ? ? ? ? ? ? ? else
>> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? submit_bh(write_op, bh);
>> ? ? ? ? ? ? ? ? ? ? ? nr_underway++;
>> ? ? ? ? ? ? ? }
>> ? ? ? ? ? ? ? bh = next;
>> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
>> index ef26043..0776564 100644
>> --- a/include/linux/buffer_head.h
>> +++ b/include/linux/buffer_head.h
>> @@ -34,6 +34,7 @@ enum bh_state_bits {
>> ? ? ? BH_Write_EIO, ? /* I/O error on write */
>> ? ? ? BH_Unwritten, ? /* Buffer is allocated on disk but not written */
>> ? ? ? BH_Quiet, ? ? ? /* Buffer Error Prinks to be quiet */
>> + ? ? BH_Meta, ? ? ? ?/* Is meta */
>>
>> ? ? ? BH_PrivateStart,/* not a state bit, but the first bit available
>> ? ? ? ? ? ? ? ? ? ? ? ?* for private allocation by other entities
>> @@ -126,6 +127,7 @@ BUFFER_FNS(Delay, delay)
>> ?BUFFER_FNS(Boundary, boundary)
>> ?BUFFER_FNS(Write_EIO, write_io_error)
>> ?BUFFER_FNS(Unwritten, unwritten)
>> +BUFFER_FNS(Meta, meta)
>>
>> ?#define bh_offset(bh) ? ? ? ? ? ? ? ?((unsigned long)(bh)->b_data & ~PAGE_MASK)
>> ?#define touch_buffer(bh) ? ? mark_page_accessed(bh->b_page)
Hi Ted, Christoph
Will you please comment on the following patch set,
[PATCH 1/2] block: add BH_Meta flag
[PATCH 2/2] ext4: annotate all meta data requests
If there is no remark, then will you please merge them to the next version.
Thanks,
Saugata
On 11 May 2012 20:32, Saugata Das <[email protected]> wrote:
> From: Saugata Das <[email protected]>
>
> Today, storage devices like eMMC has special features like data tagging
> (introduced in MMC-4.5 version) in order to improve performance of some
> specific writes. On MMC stack, data tagging is used for all writes which
> has REQ_META flag set. This patch adds the capability to add REQ_META flag
> during meta data write.
>
> Signed-off-by: Saugata Das <[email protected]>
> ---
> ?fs/buffer.c ? ? ? ? ? ? ? ? | ? 10 ++++++++--
> ?include/linux/buffer_head.h | ? ?2 ++
> ?2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 36d6665..688b38b 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1685,7 +1685,10 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
> ? ? ? ?do {
> ? ? ? ? ? ? ? ?struct buffer_head *next = bh->b_this_page;
> ? ? ? ? ? ? ? ?if (buffer_async_write(bh)) {
> - ? ? ? ? ? ? ? ? ? ? ? submit_bh(write_op, bh);
> + ? ? ? ? ? ? ? ? ? ? ? if (buffer_meta(bh))
> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? submit_bh(write_op | REQ_META, bh);
> + ? ? ? ? ? ? ? ? ? ? ? else
> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? submit_bh(write_op, bh);
> ? ? ? ? ? ? ? ? ? ? ? ?nr_underway++;
> ? ? ? ? ? ? ? ?}
> ? ? ? ? ? ? ? ?bh = next;
> @@ -1739,7 +1742,10 @@ recover:
> ? ? ? ? ? ? ? ?struct buffer_head *next = bh->b_this_page;
> ? ? ? ? ? ? ? ?if (buffer_async_write(bh)) {
> ? ? ? ? ? ? ? ? ? ? ? ?clear_buffer_dirty(bh);
> - ? ? ? ? ? ? ? ? ? ? ? submit_bh(write_op, bh);
> + ? ? ? ? ? ? ? ? ? ? ? if (buffer_meta(bh))
> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? submit_bh(write_op | REQ_META, bh);
> + ? ? ? ? ? ? ? ? ? ? ? else
> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? submit_bh(write_op, bh);
> ? ? ? ? ? ? ? ? ? ? ? ?nr_underway++;
> ? ? ? ? ? ? ? ?}
> ? ? ? ? ? ? ? ?bh = next;
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> index ef26043..0776564 100644
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -34,6 +34,7 @@ enum bh_state_bits {
> ? ? ? ?BH_Write_EIO, ? /* I/O error on write */
> ? ? ? ?BH_Unwritten, ? /* Buffer is allocated on disk but not written */
> ? ? ? ?BH_Quiet, ? ? ? /* Buffer Error Prinks to be quiet */
> + ? ? ? BH_Meta, ? ? ? ?/* Is meta */
>
> ? ? ? ?BH_PrivateStart,/* not a state bit, but the first bit available
> ? ? ? ? ? ? ? ? ? ? ? ? * for private allocation by other entities
> @@ -126,6 +127,7 @@ BUFFER_FNS(Delay, delay)
> ?BUFFER_FNS(Boundary, boundary)
> ?BUFFER_FNS(Write_EIO, write_io_error)
> ?BUFFER_FNS(Unwritten, unwritten)
> +BUFFER_FNS(Meta, meta)
>
> ?#define bh_offset(bh) ? ? ? ? ?((unsigned long)(bh)->b_data & ~PAGE_MASK)
> ?#define touch_buffer(bh) ? ? ? mark_page_accessed(bh->b_page)
> --
> 1.7.4.3
>
On 05/11/2012 06:02 PM, Saugata Das wrote:
> From: Saugata Das <[email protected]>
>
> Today, storage devices like eMMC has special features like data tagging
> (introduced in MMC-4.5 version) in order to improve performance of some
> specific writes. On MMC stack, data tagging is used for all writes which
> has REQ_META flag set. This patch adds the capability to add REQ_META flag
> during meta data write.
>
> Signed-off-by: Saugata Das <[email protected]>
> ---
> fs/buffer.c | 10 ++++++++--
> include/linux/buffer_head.h | 2 ++
> 2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 36d6665..688b38b 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1685,7 +1685,10 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
> do {
> struct buffer_head *next = bh->b_this_page;
> if (buffer_async_write(bh)) {
> - submit_bh(write_op, bh);
> + if (buffer_meta(bh))
> + submit_bh(write_op | REQ_META, bh);
> + else
> + submit_bh(write_op, bh);
Its not nice to duplicate a call site for the parameter difference
it's better to change the parameter and call the function in one
place. (an assembler call site can get big)
You can do:
+ submit_bh(write_op | (buffer_meta(bh) << __REQ_META), bh);
And also avoid a conditional inside a loop.
> nr_underway++;
> }
> bh = next;
> @@ -1739,7 +1742,10 @@ recover:
> struct buffer_head *next = bh->b_this_page;
> if (buffer_async_write(bh)) {
> clear_buffer_dirty(bh);
> - submit_bh(write_op, bh);
> + if (buffer_meta(bh))
> + submit_bh(write_op | REQ_META, bh);
> + else
> + submit_bh(write_op, bh);
Here too
Boaz
> nr_underway++;
> }
> bh = next;
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> index ef26043..0776564 100644
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -34,6 +34,7 @@ enum bh_state_bits {
> BH_Write_EIO, /* I/O error on write */
> BH_Unwritten, /* Buffer is allocated on disk but not written */
> BH_Quiet, /* Buffer Error Prinks to be quiet */
> + BH_Meta, /* Is meta */
>
> BH_PrivateStart,/* not a state bit, but the first bit available
> * for private allocation by other entities
> @@ -126,6 +127,7 @@ BUFFER_FNS(Delay, delay)
> BUFFER_FNS(Boundary, boundary)
> BUFFER_FNS(Write_EIO, write_io_error)
> BUFFER_FNS(Unwritten, unwritten)
> +BUFFER_FNS(Meta, meta)
>
> #define bh_offset(bh) ((unsigned long)(bh)->b_data & ~PAGE_MASK)
> #define touch_buffer(bh) mark_page_accessed(bh->b_page)
On 16 May 2012 18:02, Boaz Harrosh <[email protected]> wrote:
> On 05/11/2012 06:02 PM, Saugata Das wrote:
>
>> From: Saugata Das <[email protected]>
>>
>> Today, storage devices like eMMC has special features like data tagging
>> (introduced in MMC-4.5 version) in order to improve performance of some
>> specific writes. On MMC stack, data tagging is used for all writes which
>> has REQ_META flag set. This patch adds the capability to add REQ_META flag
>> during meta data write.
>>
>> Signed-off-by: Saugata Das <[email protected]>
>> ---
>> ?fs/buffer.c ? ? ? ? ? ? ? ? | ? 10 ++++++++--
>> ?include/linux/buffer_head.h | ? ?2 ++
>> ?2 files changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/buffer.c b/fs/buffer.c
>> index 36d6665..688b38b 100644
>> --- a/fs/buffer.c
>> +++ b/fs/buffer.c
>> @@ -1685,7 +1685,10 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
>> ? ? ? do {
>> ? ? ? ? ? ? ? struct buffer_head *next = bh->b_this_page;
>> ? ? ? ? ? ? ? if (buffer_async_write(bh)) {
>> - ? ? ? ? ? ? ? ? ? ? submit_bh(write_op, bh);
>> + ? ? ? ? ? ? ? ? ? ? if (buffer_meta(bh))
>> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? submit_bh(write_op | REQ_META, bh);
>> + ? ? ? ? ? ? ? ? ? ? else
>> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? submit_bh(write_op, bh);
>
>
> Its not nice to duplicate a call site for the parameter difference
> it's better to change the parameter and call the function in one
> place. (an assembler call site can get big)
>
> You can do:
> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? submit_bh(write_op | (buffer_meta(bh) << __REQ_META), bh);
>
> And also avoid a conditional inside a loop.
>
Thanks for your comments. I will take care of this in the next version.
>
>> ? ? ? ? ? ? ? ? ? ? ? nr_underway++;
>> ? ? ? ? ? ? ? }
>> ? ? ? ? ? ? ? bh = next;
>> @@ -1739,7 +1742,10 @@ recover:
>> ? ? ? ? ? ? ? struct buffer_head *next = bh->b_this_page;
>> ? ? ? ? ? ? ? if (buffer_async_write(bh)) {
>> ? ? ? ? ? ? ? ? ? ? ? clear_buffer_dirty(bh);
>> - ? ? ? ? ? ? ? ? ? ? submit_bh(write_op, bh);
>> + ? ? ? ? ? ? ? ? ? ? if (buffer_meta(bh))
>> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? submit_bh(write_op | REQ_META, bh);
>> + ? ? ? ? ? ? ? ? ? ? else
>> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? submit_bh(write_op, bh);
>
>
> Here too
>
> Boaz
>
>> ? ? ? ? ? ? ? ? ? ? ? nr_underway++;
>> ? ? ? ? ? ? ? }
>> ? ? ? ? ? ? ? bh = next;
>> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
>> index ef26043..0776564 100644
>> --- a/include/linux/buffer_head.h
>> +++ b/include/linux/buffer_head.h
>> @@ -34,6 +34,7 @@ enum bh_state_bits {
>> ? ? ? BH_Write_EIO, ? /* I/O error on write */
>> ? ? ? BH_Unwritten, ? /* Buffer is allocated on disk but not written */
>> ? ? ? BH_Quiet, ? ? ? /* Buffer Error Prinks to be quiet */
>> + ? ? BH_Meta, ? ? ? ?/* Is meta */
>>
>> ? ? ? BH_PrivateStart,/* not a state bit, but the first bit available
>> ? ? ? ? ? ? ? ? ? ? ? ?* for private allocation by other entities
>> @@ -126,6 +127,7 @@ BUFFER_FNS(Delay, delay)
>> ?BUFFER_FNS(Boundary, boundary)
>> ?BUFFER_FNS(Write_EIO, write_io_error)
>> ?BUFFER_FNS(Unwritten, unwritten)
>> +BUFFER_FNS(Meta, meta)
>>
>> ?#define bh_offset(bh) ? ? ? ? ? ? ? ?((unsigned long)(bh)->b_data & ~PAGE_MASK)
>> ?#define touch_buffer(bh) ? ? mark_page_accessed(bh->b_page)
>
>