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Date: Thu, 9 Oct 2008 13:48:34 +0530
From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To: "Theodore Ts'o" <tytso@....edu>
Cc: linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 29/42] ext4: Use readahead when reading an inode from
the inode table
On Thu, Oct 09, 2008 at 12:05:47AM -0400, Theodore Ts'o wrote:
> 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@....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(-)
Need documentation for the new mount option and the /proc tunable.
>
> 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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