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Subject[patch 6/16] buffer_boundary() for ext3


Implement buffer_boundary() for ext3.

buffer_boundary() is an I/O scheduling hint which the filesystem's
get_block() function passes up to the BIO assembly code. It is
described in fs/mpage.c

The time to read 1,000 52 kbyte files goes from 8.6 seconds down to 2.9
seconds. 52 kbytes is the worst-case size.


=====================================

--- 2.5.19/fs/ext3/inode.c~ext3-buffer_boundary Sat Jun 1 01:18:08 2002
+++ 2.5.19-akpm/fs/ext3/inode.c Sat Jun 1 01:18:08 2002
@@ -306,6 +306,8 @@ static inline int verify_chain(Indirect
* @inode: inode in question (we are only interested in its superblock)
* @i_block: block number to be parsed
* @offsets: array to store the offsets in
+ * @boundary: set this non-zero if the referred-to block is likely to be
+ * followed (on disk) by an indirect block.
*
* To store the locations of file's data ext3 uses a data structure common
* for UNIX filesystems - tree of pointers anchored in the inode, with
@@ -330,7 +332,8 @@ static inline int verify_chain(Indirect
* get there at all.
*/

-static int ext3_block_to_path(struct inode *inode, long i_block, int offsets[4])
+static int ext3_block_to_path(struct inode *inode,
+ long i_block, int offsets[4], int *boundary)
{
int ptrs = EXT3_ADDR_PER_BLOCK(inode->i_sb);
int ptrs_bits = EXT3_ADDR_PER_BLOCK_BITS(inode->i_sb);
@@ -338,26 +341,33 @@ static int ext3_block_to_path(struct ino
indirect_blocks = ptrs,
double_blocks = (1 << (ptrs_bits * 2));
int n = 0;
+ int final = 0;

if (i_block < 0) {
ext3_warning (inode->i_sb, "ext3_block_to_path", "block < 0");
} else if (i_block < direct_blocks) {
offsets[n++] = i_block;
+ final = direct_blocks;
} else if ( (i_block -= direct_blocks) < indirect_blocks) {
offsets[n++] = EXT3_IND_BLOCK;
offsets[n++] = i_block;
+ final = ptrs;
} else if ((i_block -= indirect_blocks) < double_blocks) {
offsets[n++] = EXT3_DIND_BLOCK;
offsets[n++] = i_block >> ptrs_bits;
offsets[n++] = i_block & (ptrs - 1);
+ final = ptrs;
} else if (((i_block -= double_blocks) >> (ptrs_bits * 2)) < ptrs) {
offsets[n++] = EXT3_TIND_BLOCK;
offsets[n++] = i_block >> (ptrs_bits * 2);
offsets[n++] = (i_block >> ptrs_bits) & (ptrs - 1);
offsets[n++] = i_block & (ptrs - 1);
+ final = ptrs;
} else {
ext3_warning (inode->i_sb, "ext3_block_to_path", "block > big");
}
+ if (boundary)
+ *boundary = (i_block & (ptrs - 1)) == (final - 1);
return n;
}

@@ -734,7 +744,8 @@ static int ext3_get_block_handle(handle_
Indirect *partial;
unsigned long goal;
int left;
- int depth = ext3_block_to_path(inode, iblock, offsets);
+ int boundary = 0;
+ int depth = ext3_block_to_path(inode, iblock, offsets, &boundary);
struct ext3_inode_info *ei = EXT3_I(inode);
loff_t new_size;

@@ -752,6 +763,8 @@ reread:
clear_buffer_new(bh_result);
got_it:
map_bh(bh_result, inode->i_sb, le32_to_cpu(chain[depth-1].key));
+ if (boundary)
+ set_buffer_boundary(bh_result);
/* Clean up and exit */
partial = chain+depth-1; /* the whole chain */
goto cleanup;
@@ -1875,7 +1888,7 @@ void ext3_truncate(struct inode * inode)
ext3_block_truncate_page(handle, inode->i_mapping, inode->i_size);


- n = ext3_block_to_path(inode, last_block, offsets);
+ n = ext3_block_to_path(inode, last_block, offsets, NULL);
if (n == 0)
goto out_stop; /* error */

-
-
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