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ext4: Use readahead when reading an inode from the inode table 

With modern hard drives, reading 64k takes roughly the same time as
reading a 4k block.  So request readahead for adjacent inode table
blocks to reduce the time it takes when iterating over directories
(especially when doing this in htree sort order) in a cold cache case.
With this patch, the time it takes to run "git status" on a kernel
tree after flushing the caches via "echo 3 > /proc/sys/vm/drop_caches"
is reduced by 21%.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Theodore Ts'o 2008-10-09 23:53:47 -04:00
parent 37515facd0
commit 240799cdf2
6 changed files with 100 additions and 71 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
Documentation/filesystems/ext4.txt
View File

@ -177,6 +177,11 @@ barrier=<0|1(*)> This enables/disables the use of write barriers in
your disks are battery-backed in one way or another,
disabling barriers may safely improve performance.
inode_readahead=n This tuning parameter controls the maximum
number of inode table blocks that ext4's inode
table readahead algorithm will pre-read into
the buffer cache. The default value is 32 blocks.
orlov (*) This enables the new Orlov block allocator. It is
enabled by default.
@ -252,6 +257,7 @@ stripe=n Number of filesystem blocks that mballoc will try
delalloc (*) Deferring block allocation until write-out time.
nodelalloc Disable delayed allocation. Blocks are allocation
when data is copied from user to page cache.
Data Mode
=========
There are 3 different data modes:

3
Documentation/filesystems/proc.txt
View File

@ -956,6 +956,9 @@ Table 1-10: Files in /proc/fs/ext4/<devname>
files are packed closely together. Each large file
will have its blocks allocated out of its own unique
preallocation pool.
inode_readahead Tuning parameter which controls the maximum number of
inode table blocks that ext4's inode table readahead
algorithm will pre-read into the buffer cache
..............................................................................

2
fs/ext4/ext4.h
View File

@ -790,6 +790,8 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
#define EXT4_DEF_RESUID 0
#define EXT4_DEF_RESGID 0
#define EXT4_DEF_INODE_READAHEAD_BLKS 32
/*
* Default mount options
*/

1
fs/ext4/ext4_sb.h
View File

@ -52,6 +52,7 @@ struct ext4_sb_info {
int s_desc_per_block_bits;
int s_inode_size;
int s_first_ino;
unsigned int s_inode_readahead_blks;
spinlock_t s_next_gen_lock;
u32 s_next_generation;
u32 s_hash_seed[4];

128
fs/ext4/inode.c
View File

@ -3833,41 +3833,6 @@ out_stop:
ext4_journal_stop(handle);
}
static ext4_fsblk_t ext4_get_inode_block(struct super_block *sb,
unsigned long ino, struct ext4_iloc *iloc)
{
ext4_group_t block_group;
unsigned long offset;
ext4_fsblk_t block;
struct ext4_group_desc *gdp;
if (!ext4_valid_inum(sb, ino)) {
/*
* This error is already checked for in namei.c unless we are
* looking at an NFS filehandle, in which case no error
* report is needed
*/
return 0;
}
block_group = (ino - 1) / EXT4_INODES_PER_GROUP(sb);
gdp = ext4_get_group_desc(sb, block_group, NULL);
if (!gdp)
return 0;
/*
* Figure out the offset within the block group inode table
*/
offset = ((ino - 1) % EXT4_INODES_PER_GROUP(sb)) *
EXT4_INODE_SIZE(sb);
block = ext4_inode_table(sb, gdp) +
(offset >> EXT4_BLOCK_SIZE_BITS(sb));
iloc->block_group = block_group;
iloc->offset = offset & (EXT4_BLOCK_SIZE(sb) - 1);
return block;
}
/*
* ext4_get_inode_loc returns with an extra refcount against the inode's
* underlying buffer_head on success. If 'in_mem' is true, we have all
@ -3877,18 +3842,34 @@ static ext4_fsblk_t ext4_get_inode_block(struct super_block *sb,
static int __ext4_get_inode_loc(struct inode *inode,
struct ext4_iloc *iloc, int in_mem)
{
ext4_fsblk_t block;
struct ext4_group_desc *gdp;
struct buffer_head *bh;
struct super_block *sb = inode->i_sb;
ext4_fsblk_t block;
int inodes_per_block, inode_offset;
block = ext4_get_inode_block(inode->i_sb, inode->i_ino, iloc);
if (!block)
iloc->bh = 0;
if (!ext4_valid_inum(sb, inode->i_ino))
return -EIO;
bh = sb_getblk(inode->i_sb, block);
iloc->block_group = (inode->i_ino - 1) / EXT4_INODES_PER_GROUP(sb);
gdp = ext4_get_group_desc(sb, iloc->block_group, NULL);
if (!gdp)
return -EIO;
/*
* Figure out the offset within the block group inode table
*/
inodes_per_block = (EXT4_BLOCK_SIZE(sb) / EXT4_INODE_SIZE(sb));
inode_offset = ((inode->i_ino - 1) %
EXT4_INODES_PER_GROUP(sb));
block = ext4_inode_table(sb, gdp) + (inode_offset / inodes_per_block);
iloc->offset = (inode_offset % inodes_per_block) * EXT4_INODE_SIZE(sb);
bh = sb_getblk(sb, block);
if (!bh) {
ext4_error (inode->i_sb, "ext4_get_inode_loc",
"unable to read inode block - "
"inode=%lu, block=%llu",
ext4_error(sb, "ext4_get_inode_loc", "unable to read "
"inode block - inode=%lu, block=%llu",
inode->i_ino, block);
return -EIO;
}
@ -3917,28 +3898,12 @@ static int __ext4_get_inode_loc(struct inode *inode,
*/
if (in_mem) {
struct buffer_head *bitmap_bh;
struct ext4_group_desc *desc;
int inodes_per_buffer;
int inode_offset, i;
ext4_group_t block_group;
int start;
int i, start;
block_group = (inode->i_ino - 1) /
EXT4_INODES_PER_GROUP(inode->i_sb);
inodes_per_buffer = bh->b_size /
EXT4_INODE_SIZE(inode->i_sb);
inode_offset = ((inode->i_ino - 1) %
EXT4_INODES_PER_GROUP(inode->i_sb));
start = inode_offset & ~(inodes_per_buffer - 1);
start = inode_offset & ~(inodes_per_block - 1);
/* Is the inode bitmap in cache? */
desc = ext4_get_group_desc(inode->i_sb,
block_group, NULL);
if (!desc)
goto make_io;
bitmap_bh = sb_getblk(inode->i_sb,
ext4_inode_bitmap(inode->i_sb, desc));
bitmap_bh = sb_getblk(sb, ext4_inode_bitmap(sb, gdp));
if (!bitmap_bh)
goto make_io;
@ -3951,14 +3916,14 @@ static int __ext4_get_inode_loc(struct inode *inode,
brelse(bitmap_bh);
goto make_io;
}
for (i = start; i < start + inodes_per_buffer; i++) {
for (i = start; i < start + inodes_per_block; i++) {
if (i == inode_offset)
continue;
if (ext4_test_bit(i, bitmap_bh->b_data))
break;
}
brelse(bitmap_bh);
if (i == start + inodes_per_buffer) {
if (i == start + inodes_per_block) {
/* all other inodes are free, so skip I/O */
memset(bh->b_data, 0, bh->b_size);
set_buffer_uptodate(bh);
@ -3968,6 +3933,36 @@ static int __ext4_get_inode_loc(struct inode *inode,
}
make_io:
/*
* If we need to do any I/O, try to pre-readahead extra
* blocks from the inode table.
*/
if (EXT4_SB(sb)->s_inode_readahead_blks) {
ext4_fsblk_t b, end, table;
unsigned num;
table = ext4_inode_table(sb, gdp);
/* Make sure s_inode_readahead_blks is a power of 2 */
while (EXT4_SB(sb)->s_inode_readahead_blks &
(EXT4_SB(sb)->s_inode_readahead_blks-1))
EXT4_SB(sb)->s_inode_readahead_blks =
(EXT4_SB(sb)->s_inode_readahead_blks &
(EXT4_SB(sb)->s_inode_readahead_blks-1));
b = block & ~(EXT4_SB(sb)->s_inode_readahead_blks-1);
if (table > b)
b = table;
end = b + EXT4_SB(sb)->s_inode_readahead_blks;
num = EXT4_INODES_PER_GROUP(sb);
if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
EXT4_FEATURE_RO_COMPAT_GDT_CSUM))
num -= le16_to_cpu(gdp->bg_itable_unused);
table += num / inodes_per_block;
if (end > table)
end = table;
while (b <= end)
sb_breadahead(sb, b++);
}
/*
* There are other valid inodes in the buffer, this inode
* has in-inode xattrs, or we don't have this inode in memory.
@ -3978,10 +3973,9 @@ make_io:
submit_bh(READ_META, bh);
wait_on_buffer(bh);
if (!buffer_uptodate(bh)) {
ext4_error(inode->i_sb, "ext4_get_inode_loc",
"unable to read inode block - "
"inode=%lu, block=%llu",
inode->i_ino, block);
ext4_error(sb, __func__,
"unable to read inode block - inode=%lu, "
"block=%llu", inode->i_ino, block);
brelse(bh);
return -EIO;
}

27
fs/ext4/super.c
View File

@ -515,8 +515,10 @@ static void ext4_put_super(struct super_block *sb)
mark_buffer_dirty(sbi->s_sbh);
ext4_commit_super(sb, es, 1);
}
if (sbi->s_proc)
if (sbi->s_proc) {
remove_proc_entry("inode_readahead_blks", sbi->s_proc);
remove_proc_entry(sb->s_id, ext4_proc_root);
}
for (i = 0; i < sbi->s_gdb_count; i++)
brelse(sbi->s_group_desc[i]);
@ -779,6 +781,10 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
else if (test_opt(sb, DATA_FLAGS) == EXT4_MOUNT_WRITEBACK_DATA)
seq_puts(seq, ",data=writeback");
if (sbi->s_inode_readahead_blks != EXT4_DEF_INODE_READAHEAD_BLKS)
seq_printf(seq, ",inode_readahead_blks=%u",
sbi->s_inode_readahead_blks);
ext4_show_quota_options(seq, sb);
return 0;
}
@ -913,6 +919,7 @@ enum {
Opt_ignore, Opt_barrier, Opt_err, Opt_resize, Opt_usrquota,
Opt_grpquota, Opt_extents, Opt_noextents, Opt_i_version,
Opt_mballoc, Opt_nomballoc, Opt_stripe, Opt_delalloc, Opt_nodelalloc,
Opt_inode_readahead_blks
};
static match_table_t tokens = {
@ -973,6 +980,7 @@ static match_table_t tokens = {
{Opt_resize, "resize"},
{Opt_delalloc, "delalloc"},
{Opt_nodelalloc, "nodelalloc"},
{Opt_inode_readahead_blks, "inode_readahead_blks=%u"},
{Opt_err, NULL},
};
@ -1381,6 +1389,13 @@ set_qf_format:
case Opt_delalloc:
set_opt(sbi->s_mount_opt, DELALLOC);
break;
case Opt_inode_readahead_blks:
if (match_int(&args[0], &option))
return 0;
if (option < 0 || option > (1 << 30))
return 0;
sbi->s_inode_readahead_blks = option;
break;
default:
printk(KERN_ERR
"EXT4-fs: Unrecognized mount option \"%s\" "
@ -1938,6 +1953,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
sbi->s_mount_opt = 0;
sbi->s_resuid = EXT4_DEF_RESUID;
sbi->s_resgid = EXT4_DEF_RESGID;
sbi->s_inode_readahead_blks = EXT4_DEF_INODE_READAHEAD_BLKS;
sbi->s_sb_block = sb_block;
unlock_kernel();
@ -2234,6 +2250,11 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
if (ext4_proc_root)
sbi->s_proc = proc_mkdir(sb->s_id, ext4_proc_root);
if (sbi->s_proc)
proc_create_data("inode_readahead_blks", 0644, sbi->s_proc,
&ext4_ui_proc_fops,
&sbi->s_inode_readahead_blks);
bgl_lock_init(&sbi->s_blockgroup_lock);
for (i = 0; i < db_count; i++) {
@ -2513,8 +2534,10 @@ failed_mount2:
brelse(sbi->s_group_desc[i]);
kfree(sbi->s_group_desc);
failed_mount:
if (sbi->s_proc)
if (sbi->s_proc) {
remove_proc_entry("inode_readahead_blks", sbi->s_proc);
remove_proc_entry(sb->s_id, ext4_proc_root);
}
#ifdef CONFIG_QUOTA
for (i = 0; i < MAXQUOTAS; i++)
kfree(sbi->s_qf_names[i]);