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Subject[PATCH 29/42] ext4: Use readahead when reading an inode from the inode table
Date
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>
---
fs/ext4/ext4.h | 2 +
fs/ext4/ext4_sb.h | 1 +
fs/ext4/inode.c | 134 +++++++++++++++++++++++++---------------------------
fs/ext4/super.c | 27 ++++++++++-
4 files changed, 92 insertions(+), 72 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 163c445..922d187 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -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
*/
diff --git a/fs/ext4/ext4_sb.h b/fs/ext4/ext4_sb.h
index f92af01..94e0757 100644
--- a/fs/ext4/ext4_sb.h
+++ b/fs/ext4/ext4_sb.h
@@ -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];
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 22fcbb6..ef4ca3d 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -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
@@ -3877,19 +3842,35 @@ 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 buffer_head *bh;
+ 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;
+
+ iloc->bh = 0;
+ if (!ext4_valid_inum(sb, inode->i_ino))
+ return -EIO;

- block = ext4_get_inode_block(inode->i_sb, inode->i_ino, iloc);
- if (!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;

- bh = sb_getblk(inode->i_sb, block);
+ /*
+ * 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",
- inode->i_ino, block);
+ ext4_error(sb, "ext4_get_inode_loc", "unable to read "
+ "inode block - inode=%lu, block=%llu",
+ inode->i_ino, block);
return -EIO;
}
if (!buffer_uptodate(bh)) {
@@ -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;
-
- 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);
+ int i, start;

- /* Is the inode bitmap in cache? */
- desc = ext4_get_group_desc(inode->i_sb,
- block_group, NULL);
- if (!desc)
- goto make_io;
+ start = inode_offset & ~(inodes_per_block - 1);

- bitmap_bh = sb_getblk(inode->i_sb,
- ext4_inode_bitmap(inode->i_sb, desc));
+ /* Is the inode bitmap in cache? */
+ 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);
@@ -3969,6 +3934,36 @@ 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.
* Read the block from disk.
@@ -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;
}
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 9f5468f..6583aee 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -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]);
--
1.5.6.1.205.ge2c7.dirty


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