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SubjectRe: [PATCH] change b_size to size_t
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On Thu, 2006-02-23 at 11:32 -0500, Benjamin LaHaise wrote:
> On Thu, Feb 23, 2006 at 08:28:12AM -0800, Badari Pulavarty wrote:
> > Here is the updated version of the patch, which changes
> > buffer_head.b_size to size_t to support mapping large
> > amount of disk blocks (for large IOs).
>
> Your patch doesn't seem to be inline, so I can't quote it. Several
> problems: on 64 bit platforms you introduced 4 bytes of padding into
> buffer_head. atomic_t only takes up 4 byte, while size_t is 8 byte
> aligned.

I moved stuff around, but still see 96 bytes (8 byte increase) for
the structure. What am I doing wrong ? Can you check ?

> This is a waste of memory, imo, seeing as the vast majority
> of systems out there will not be doing 4GB+ ios any time soon.

Yep. I agree. I was modifying get_block() to take b_size as the amount
of disk mapping requested, so I can get rid of ->get_blocks() and also
add support for mpage_readpages() and mapge_writepages() to deal with
multiple blocks. XFS seems to be requesting >4GB IOs, but doing 4GB
IOs through DIO today and planning to see bigger IOs in future.

Since "buffer_head" is not a primary structure used for IO anymore +
this change affect only 64-bit machines, its worth doing this ?

> Also, the cast to unsigned long long for size_t is pretty atrocious.
> Cast to unsigned long if anything, as size_t is unsigned long on all
> platforms linux runs on.

Okay. Changed it to (unsigned long) instead. I was just following
sector_t :(

Thanks,
Badari

Increase the size of the buffer_head b_size field for 64 bit
platforms. Update some old and moldy comments in and around
the structure as well.

The b_size increase allows us to perform larger mappings and
allocations for large I/O requests from userspace, which tie
in with other changes allowing the get_block_t() interface to
map multiple blocks at once.

Signed-off-by: Nathan Scott <nathans@sgi.com>
Signed-off-by: Badari Pulavary <pbadari@us.ibm.com>

Index: linux-2.6.16-rc4/include/linux/buffer_head.h
===================================================================
--- linux-2.6.16-rc4.orig/include/linux/buffer_head.h 2006-02-17
14:23:45.000000000 -0800
+++ linux-2.6.16-rc4/include/linux/buffer_head.h 2006-02-23
09:00:06.000000000 -0800
@@ -46,20 +46,23 @@ struct address_space;
typedef void (bh_end_io_t)(struct buffer_head *bh, int uptodate);

/*
- * Keep related fields in common cachelines. The most commonly
accessed
- * field (b_state) goes at the start so the compiler does not generate
- * indexed addressing for it.
+ * Historically, a buffer_head was used to map a single block
+ * within a page, and of course as the unit of I/O through the
+ * filesystem and block layers. Nowadays the basic I/O unit
+ * is the bio, and buffer_heads are used for extracting block
+ * mappings (via a get_block_t call), for tracking state within
+ * a page (via a page_mapping) and for wrapping bio submission
+ * for backward compatibility reasons (e.g. submit_bh).
*/
struct buffer_head {
- /* First cache line: */
unsigned long b_state; /* buffer state bitmap (see above) */
struct buffer_head *b_this_page;/* circular list of page's buffers */
struct page *b_page; /* the page this bh is mapped to */
- atomic_t b_count; /* users using this block */
- u32 b_size; /* block size */
+ char *b_data; /* pointer to data within the page */

- sector_t b_blocknr; /* block number */
- char *b_data; /* pointer to data block */
+ size_t b_size; /* size of mapping */
+ sector_t b_blocknr; /* start block number */
+ atomic_t b_count; /* users using this buffer_head */

struct block_device *b_bdev;
bh_end_io_t *b_end_io; /* I/O completion */
Index: linux-2.6.16-rc4/fs/buffer.c
===================================================================
--- linux-2.6.16-rc4.orig/fs/buffer.c 2006-02-17 14:23:45.000000000
-0800
+++ linux-2.6.16-rc4/fs/buffer.c 2006-02-23 08:55:18.000000000 -0800
@@ -432,7 +432,8 @@ __find_get_block_slow(struct block_devic
printk("__find_get_block_slow() failed. "
"block=%llu, b_blocknr=%llu\n",
(unsigned long long)block, (unsigned long long)bh->b_blocknr);
- printk("b_state=0x%08lx, b_size=%u\n", bh->b_state, bh->b_size);
+ printk("b_state=0x%08lx, b_size=%lu\n", bh->b_state,
+ (unsigned long)bh->b_size);
printk("device blocksize: %d\n", 1 << bd_inode->i_blkbits);
}
out_unlock:
Index: linux-2.6.16-rc4/fs/reiserfs/prints.c
===================================================================
--- linux-2.6.16-rc4.orig/fs/reiserfs/prints.c 2006-02-17
14:23:45.000000000 -0800
+++ linux-2.6.16-rc4/fs/reiserfs/prints.c 2006-02-23 08:56:17.000000000
-0800
@@ -143,8 +143,8 @@ static void sprintf_buffer_head(char *bu
char b[BDEVNAME_SIZE];

sprintf(buf,
- "dev %s, size %d, blocknr %llu, count %d, state 0x%lx, page %p, (%s,
%s, %s)",
- bdevname(bh->b_bdev, b), bh->b_size,
+ "dev %s, size %ld, blocknr %llu, count %d, state 0x%lx, page %p, (%s,
%s, %s)",
+ bdevname(bh->b_bdev, b), (unsigned long)bh->b_size,
(unsigned long long)bh->b_blocknr, atomic_read(&(bh->b_count)),
bh->b_state, bh->b_page,
buffer_uptodate(bh) ? "UPTODATE" : "!UPTODATE",
Index: linux-2.6.16-rc4/fs/ocfs2/journal.c
===================================================================
--- linux-2.6.16-rc4.orig/fs/ocfs2/journal.c 2006-02-17
14:23:45.000000000 -0800
+++ linux-2.6.16-rc4/fs/ocfs2/journal.c 2006-02-23 08:56:55.000000000
-0800
@@ -377,12 +377,12 @@ int ocfs2_journal_access(struct ocfs2_jo
BUG_ON(!bh);
BUG_ON(!(handle->flags & OCFS2_HANDLE_STARTED));

- mlog_entry("bh->b_blocknr=%llu, type=%d (\"%s\"), bh->b_size = %hu\n",
+ mlog_entry("bh->b_blocknr=%llu, type=%d (\"%s\"), bh->b_size = %lu\n",
(unsigned long long)bh->b_blocknr, type,
(type == OCFS2_JOURNAL_ACCESS_CREATE) ?
"OCFS2_JOURNAL_ACCESS_CREATE" :
"OCFS2_JOURNAL_ACCESS_WRITE",
- bh->b_size);
+ (unsigned long)bh->b_size);

/* we can safely remove this assertion after testing. */
if (!buffer_uptodate(bh)) {
Increase the size of the buffer_head b_size field for 64 bit
platforms. Update some old and moldy comments in and around
the structure as well.

The b_size increase allows us to perform larger mappings and
allocations for large I/O requests from userspace, which tie
in with other changes allowing the get_block_t() interface to
map multiple blocks at once.

Signed-off-by: Nathan Scott <nathans@sgi.com>
Signed-off-by: Badari Pulavary <pbadari@us.ibm.com>

Index: linux-2.6.16-rc4/include/linux/buffer_head.h
===================================================================
--- linux-2.6.16-rc4.orig/include/linux/buffer_head.h 2006-02-17 14:23:45.000000000 -0800
+++ linux-2.6.16-rc4/include/linux/buffer_head.h 2006-02-23 09:00:06.000000000 -0800
@@ -46,20 +46,23 @@ struct address_space;
typedef void (bh_end_io_t)(struct buffer_head *bh, int uptodate);

/*
- * Keep related fields in common cachelines. The most commonly accessed
- * field (b_state) goes at the start so the compiler does not generate
- * indexed addressing for it.
+ * Historically, a buffer_head was used to map a single block
+ * within a page, and of course as the unit of I/O through the
+ * filesystem and block layers. Nowadays the basic I/O unit
+ * is the bio, and buffer_heads are used for extracting block
+ * mappings (via a get_block_t call), for tracking state within
+ * a page (via a page_mapping) and for wrapping bio submission
+ * for backward compatibility reasons (e.g. submit_bh).
*/
struct buffer_head {
- /* First cache line: */
unsigned long b_state; /* buffer state bitmap (see above) */
struct buffer_head *b_this_page;/* circular list of page's buffers */
struct page *b_page; /* the page this bh is mapped to */
- atomic_t b_count; /* users using this block */
- u32 b_size; /* block size */
+ char *b_data; /* pointer to data within the page */

- sector_t b_blocknr; /* block number */
- char *b_data; /* pointer to data block */
+ size_t b_size; /* size of mapping */
+ sector_t b_blocknr; /* start block number */
+ atomic_t b_count; /* users using this buffer_head */

struct block_device *b_bdev;
bh_end_io_t *b_end_io; /* I/O completion */
Index: linux-2.6.16-rc4/fs/buffer.c
===================================================================
--- linux-2.6.16-rc4.orig/fs/buffer.c 2006-02-17 14:23:45.000000000 -0800
+++ linux-2.6.16-rc4/fs/buffer.c 2006-02-23 08:55:18.000000000 -0800
@@ -432,7 +432,8 @@ __find_get_block_slow(struct block_devic
printk("__find_get_block_slow() failed. "
"block=%llu, b_blocknr=%llu\n",
(unsigned long long)block, (unsigned long long)bh->b_blocknr);
- printk("b_state=0x%08lx, b_size=%u\n", bh->b_state, bh->b_size);
+ printk("b_state=0x%08lx, b_size=%lu\n", bh->b_state,
+ (unsigned long)bh->b_size);
printk("device blocksize: %d\n", 1 << bd_inode->i_blkbits);
}
out_unlock:
Index: linux-2.6.16-rc4/fs/reiserfs/prints.c
===================================================================
--- linux-2.6.16-rc4.orig/fs/reiserfs/prints.c 2006-02-17 14:23:45.000000000 -0800
+++ linux-2.6.16-rc4/fs/reiserfs/prints.c 2006-02-23 08:56:17.000000000 -0800
@@ -143,8 +143,8 @@ static void sprintf_buffer_head(char *bu
char b[BDEVNAME_SIZE];

sprintf(buf,
- "dev %s, size %d, blocknr %llu, count %d, state 0x%lx, page %p, (%s, %s, %s)",
- bdevname(bh->b_bdev, b), bh->b_size,
+ "dev %s, size %ld, blocknr %llu, count %d, state 0x%lx, page %p, (%s, %s, %s)",
+ bdevname(bh->b_bdev, b), (unsigned long)bh->b_size,
(unsigned long long)bh->b_blocknr, atomic_read(&(bh->b_count)),
bh->b_state, bh->b_page,
buffer_uptodate(bh) ? "UPTODATE" : "!UPTODATE",
Index: linux-2.6.16-rc4/fs/ocfs2/journal.c
===================================================================
--- linux-2.6.16-rc4.orig/fs/ocfs2/journal.c 2006-02-17 14:23:45.000000000 -0800
+++ linux-2.6.16-rc4/fs/ocfs2/journal.c 2006-02-23 08:56:55.000000000 -0800
@@ -377,12 +377,12 @@ int ocfs2_journal_access(struct ocfs2_jo
BUG_ON(!bh);
BUG_ON(!(handle->flags & OCFS2_HANDLE_STARTED));

- mlog_entry("bh->b_blocknr=%llu, type=%d (\"%s\"), bh->b_size = %hu\n",
+ mlog_entry("bh->b_blocknr=%llu, type=%d (\"%s\"), bh->b_size = %lu\n",
(unsigned long long)bh->b_blocknr, type,
(type == OCFS2_JOURNAL_ACCESS_CREATE) ?
"OCFS2_JOURNAL_ACCESS_CREATE" :
"OCFS2_JOURNAL_ACCESS_WRITE",
- bh->b_size);
+ (unsigned long)bh->b_size);

/* we can safely remove this assertion after testing. */
if (!buffer_uptodate(bh)) {
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