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>

1 files changed, 25 insertions, 2 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 9f5468fb06da..6583aee5177f 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]);